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THE PRACTICAL METHODS OF 
ORGANIC CHEMISTRY 



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THE PRACTICAL METHODS 



OF 



ORGANIC CHEMISTRY 



BY 



LUDWIG GATTERMANN, Ph.D. 

PROFESSOR IN THE UNIVERSITY OF FREIBURG 



WITH NUMEROUS ILLUSTRATIONS 



TRANSLATED BY 

WILLIAM B. SCHOBER, Ph.D. 

INSTRUCTOR IN ORGANIC CHEMISTRY IN LEHIGH UNIVERSITY 



AUTHORISED TRANSLATION 
THE SECOND AMERICAN FROM THE FOURTH GERMAN EDITION 



THE MACMILLAN COMPANY 

LONDON : MACMILLAN & CO., LTD. 
1901 

All rights reserved 



Cvfy 



oS> 



^ 



THF UBRARY OF 
CONGRESS, 

Two Copies Receiveo 

SEP. 20 1901 



CLASS ^XXot No 
COPY A. 



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Copyright, 1896, 1901, 
By THE MACMILLAN COMPANY. 



Nortoooti 33tess 

J. S. Cushing & Co. — Berwick & Smith 
Norwood Mass. U.S.A. 



Tym czarownym rekom, ktorych 
dotkniecie pok6j pozynosi. 



TRANSLATOR'S PREFACE 



The success of Professor Gattermann's book in the original 
has warranted its reproduction in English. The translation is 
intended for those students of chemistry who have not yet 
become sufficiently familiar with scientific German to be able 
to read it accurately without constant reference to a dictionary. 
To such students this translation is offered, in the hope that it 
will increase their interest in the science without causing a cor- 
responding decrease in their efforts to acquire a knowledge of 
German, which is indispensable to every well-trained chemist. 

My grateful acknowledgments are due to my colleague, Dr. 
H. M. Ullmann, for many valuable suggestions, and to Professor 
Gattermann for his courtesy in pointing out several inaccuracies 
in the German edition. 

WILLIAM B. SCHOBER. 
South Bethlehem, Pennsylvania, 
April, 1896. 



PREFACE 



The present book has resulted primarily from the private needs 
of the author. If one is obliged to initiate a large number of 
students at the same time into organic laboratory work, it is 
frequently impossible, even with the best intentions, to direct the 
attention of each individual to the innumerable details of labo- 
ratory methods. In order that students, even in the absence of 
the instructor, can gain the assistance necessary for the carrying 
out of the common operations, a General Part, dealing with 
crystallisation, distillation, drying, analytical operations, etc., is 
given before the special directions for Preparations. In the 
composition of this General Part, it has been considered of 
more value to describe the most important operations in such 
a way that the beginner may be able to carry out the directions 
independently, rather than to give as fully as possible the numer- 
ous modifications of individual operations. In the Special Part, 
to each preparation are added general observations, which relate 
to the character and general significance of the reaction carried 
out in practice ; and the result follows, that the student during 
the period given to laboratory work, becomes familiar with the 
most varied theoretical knowledge, which, acquired under these 
conditions adheres more firmly, as is well known, than if that 
knowledge were obtained exclusively from a purely theoretical 



viii PREFACE 

book. And so the author hopes that his book, along with the 
excellent " Introductions " of E. Fischer and Levy, may here and 
there win some friends. 

For the assistance given by his colleagues, in pointing out 
deficiencies of his work, the author will always be grateful. 

GATTERMANN. 

Heidelberg, August, 1894. 



PREFACE TO THE SECOND AMERICAN 
EDITION 



In the preparation of this new edition advantage has been 
taken of the opportunity offered to correct a number Of errors 
in the first edition, and to make the text a reproduction of 
the fourth German edition of Professor Gattermann's book. In 
many cases the laboratory directions have been improved, a 
number of new illustrations have been added, and the Special 
Part now includes methods for the preparation of glycol, di- 
methylcyclohexenone, s-xylenol, phenylhydroxylamine, nitroso- 
benzene, p-tolyl aldehyde (Gattermann-Koch synthesis), salicylic 
aldehyde (Reimer and Tiemann's oxyaldehyde synthesis), cuprous 
chloride, the decomposition of inactive mandelic acid into its 
active constituents, and a zinc dust determination. The prepara- 
tions of acetylene and acetylene tetrabromide have been omitted. 

WILLIAM B. SCHOBER. 
South Bethlehem, Pennsylvania, 
May, 1 90 1. 



CONTENTS 

GENERAL PART 

PAGE 

Crystallisation I 

Sublimation • . 14 

Distillation 16 

Distillation with Steam 37 

Separation of Liquid Mixtures. Separation by Extraction. Salting Out 41 

Decolourising. Removal of Tarry Matter -45 

Drying 47 

Filtration 51 

Heating under Pressure 58 

Melting-point 66 

Drying and Cleaning of Vessels 70 

ORGANIC ANALYTICAL METHODS 

Detection of Carbon, Hydrogen, Nitrogen, Sulphur, and the Halogens . 72 

Quantitative Determination of the Halogens. Carius' Method . . 75 
Quantitative Determination of Sulphur. Carius' Method . . .81 

Quantitative Determination of Nitrogen. Dumas' Method ... 85 

Quantitative Determination of Carbon and Hydrogen. Liebig's Method 98 

SPECIAL PART 
I. ALIPHATIC SERIES 

1. Reaction: The Replacement of an Alcoholic Hydroxyl Group by a 

Halogen 112 

2. Reaction: Preparation of an Acid-Chloride from the Acid . .121 

3. Reaction : Preparation of an Anhydride from the Acid-Chloride and 

the Sodium Salt of the Acid 127 



xii CONTENTS 

PAGE 

4. Reaction : Preparation of an Acid- Amide from the Ammonium Salt 

of the Acid 131 

5. Reaction: Preparation of an Acid-Nitrile from an Acid-Amide . 135 

6. Reaction: Preparation of an Acid-Ester from the Acid and Alcohol 137 

7. Reaction: Substitution of Hydrogen by Chlorine . . . .139 

8. Reaction: Oxidation of a Primary Alcohol to an Aldehyde . .143 

9. Reaction : Preparation of a Primary Amine from an Acid-Amide of 

the next Higher Series 151 

10. Reaction : Syntheses of Ketone Acid-Esters and Polyketones with 

Sodium and Sodium Alcoholate 155 

11. Reaction: Syntheses of the Homologues of Acetic Acid by means of 

Malonic Ester 161 

12. Reaction: Preparation of a Hydrocarbon of the Ethylene Series by 

the Elimination of Water from an Alcohol. Union with Bromine 166 

13. Reaction: Replacement of Halogen Atoms by Alcoholic Hydroxyl 

Groups . . . . . 171 

TRANSITION FROM THE ALIPHATIC TO THE AROMATIC 

SERIES 

Dimethylcyclohexenone and s-Xylenol from Ethylidenebisacetacetic Ester 

(Ring Closing in a 1.5 Diketone) 176 

II. AROMATIC SERIES 

1. Reaction: Nitration of a Hydrocarbon 185 

2. Reaction: Reduction of a Nitro-Compound to an Amine . .188 

3. Reaction : (a) Reduction of a Nitro-Compound to a Hydroxylamine 

Derivative. (<£) Oxidation of a Hydroxylamine Derivative to a 
Nitroso-Compound 196 

4. Reaction : Reduction of a Nitro-Compound to an Azoxy-, Azo-, or 

Hydrazo-Compound 199 

5. Reaction : Preparation of a Thiourea and a Mustard Oil from Car- 

bon Disulphide and a Primary Amine 205 

6. Reaction : Sulphonation of an Amine 208 

7. Reaction : Replacement of the Amido- and Diazo-Groups by Hy- 

drogen 210 



CONTENTS xiii 



PAGE 



8. Reaction: Replacement of the Diazo-Group by Hydroxyl . . 216 

9. Reaction: Replacement of a Diazo-Group by Iodine . . .217 

10. Reaction : Replacement of a Diazo-Group by Chlorine, Bromine, or 

Cyanogen 221 

11. Reaction: (a) Reduction of a Diazo-Compound to a Hydrazine. 

(5) Replacement of the Hydrazine-Radical by Hydrogen . . 223 

12. Reaction: (a) Preparation of an Azo-Dye from a Diazo-Compound 

and an Amine, {b) Reduction of the Azo-Compound . , 229 

13. Reaction: Preparation of a Diazoamido-Compound . . . 235 

14. Reaction : The Molecular Transformation of a Diazoamido-Com- 

pound into an Amidoazo-Compound 238 

15. Reaction: Oxidation of an Amine to a Quinone .... 239 

16. Reaction: Reduction of a Quinone to a Hydroquinone . . . 243 

17. Reaction: Bromination of an Aromatic Compound . . . 244 

18. Reaction: Fittig's Synthesis of a Hydrocarbon .... 249 

19. Reaction: Sulphonation of an Aromatic Hydrocarbon (I) . . 253 

20. Reaction : Reduction of a Sulphonchloride to a Sulphinic Acid 

or to a Thiophenol 258 

21. Reaction: Sulphonation of an Aromatic Hydrocarbon (II) . . 261 

22. Reaction : Conversion of a Sulphonic Acid into a Phenol . . 264 

23. Reaction : Nitration of a Phenol 267 

24. Reaction : (a) Chlorination of a Side-Chain of a Hydrocarbon. 

(b) Conversion of a Dichloride into an Aldehyde . . . 269 

25. Reaction: Simultaneous Oxidation and Reduction of an Aldehyde 

under the Influence of Concentrated Potassium Hydroxide . . 274 

26. Reaction : Condensation of an Aldehyde by Potassium Cyanide to a 

Benzoin 276 

Oxidation of a Benzoin to a Benzil 278 

Addition of Hydrocyanic Acid to an Aldehyde . . 279 

Perkin's Synthesis of Cinnamic Acid .... 285 

Addition of Hydrogen to an Ethylene Derivative . . 288 
Preparation of an Aromatic Acid-Chloride from the Acid 

and Phosphorus Pentachloride 289 

32. Reaction : The Schotten-Baumann Reaction for the Recognition of 

Compounds containing the Amido-, Imido-, or Hydroxyl-Group . 290 



27. 


Reaction 


28. 


Reaction 


29. 


Reaction 


30. 


Reaction 


3i- 


Reaction 



xiv CONTENTS 

PAGE 

33. Reaction: (a) Friedel and Crafts' Ketone Synthesis, (b) Prepa- 

ration of an Oxime. (<:) Beckmann's Transformation of an 

Oxime 292 

34. Reaction : Reduction of a Ketone to a Hydrocarbon . . . 301 

35. Reaction : Aldehyde Synthesis. Gattermann-Koch . . . 303 

36. Reaction : Saponification of an Acid-Nitrile 307 

37. Reaction : Oxidation of the Side-Chain of an Aromatic Compound . 309 

38. Reaction: Synthesis of Oxyaldehydes. Reimer and Tiemann . 312 

39. Reaction: Kolbe's Synthesis of Oxyacids 316 

40. Reaction : Preparation of a Dye of the Malachite Green Series . 320 

41. Reaction: Condensation of Phthalic Anhydride with a Phenol to 

form a Phthalein . . . . 323 

42. Reaction : Condensation of Michler's Ketone with an Amine to a 

Dye of the Fuchsine Series 330 

43. Reaction : Condensation of Phthalic Anhydride with a Phenol to an 

Anthraquinone Derivative 331 

44. Reaction : Alizarin from Sodium /3-Anthraquinonemonosulphonate . 333 

45. Reaction : Zinc Dust Distillation 335 

III. PYRIDINE OR QUINOLINE SERIES 

1. Reaction: The Pyridine Synthesis of Hantzsch .... 337 

2. Reaction: Skraup's Quinoline Synthesis . . . . . . 340 

IV. INORGANIC PART 

1. Chlorine 343 

2. Hydrochloric Acid 343 

3. Hydrobromic Acid 345 

4. Hydriodic Acid 345 

5. Ammonia . . . 348 

6. Nitrous Acid 348 

7. Phosphorus Trichloride 348 

8. Phosphorus Oxychloride 35° 

9. Phosphorus Pentachloride 35° 

10. Sulphurous Acid • 35 1 



CONTENTS XV 

PAGE 

11. Sodium 351 

12. Aluminium Chloride 352 

13. Lead Peroxide 354 

14. Cuprous Chloride 355 

15. Determination of the Value of Zinc Dust 356 

Index 357 

Abbreviations . 360 



THE PRACTICAL METHODS OF ORGANIC 
CHEMISTRY 



«<*:< 



GENERAL PART 



The compounds directly obtained by means of chemical reac- 
tions are, only in rare cases, pure ; they must therefore be 
subjected to a process of purification before they can be further 
utilised. For this purpose the operations most frequently em- 
ployed are : 

i . Crystallisation. 

2. Sublimation. 

3. Distillation. 



CRYSTALLISATION 

Methods of Crystallisation. — The crude solid product obtained 
directly as the result of a reaction is generally amorphous or not 
well crystallised. In order to obtain the compound in uniform, 
well-defined crystals, as well as to separate it from impurities like 
filter-fibres, inorganic substances, by-products, etc., it is dissolved, 
usually with the aid of heat, in a proper solvent, filtered from the 
impurities remaining undissolved, and allowed to cool gradually. 
The dissolved compound then separates out in a crystallised form, 
while the dissolved impurities are retained by the mother-liquor. 
(Crystallisation by Cooling.) Many compounds are so easily 
soluble in all solvents, even at the ordinary temperature, that 



2 GENERAL PART 

they do not separate from their solutions on mere cooling. 
In this case, in order to obtain crystals, a portion of the sol- 
vent must be allowed to evaporate. ( Crystallisation by Evapo- 
ration.) 

Solvents.— As solvents for organic compounds, the following 
substances are principally used : 

Class I. Water, 
Alcohol, 
Ether, 

Ligroin (Petroleum Ether), 
Glacial Acetic Acid, 
Benzene. 

Also mixtures of these : 

Class II. Water + Alcohol, 

Water -f- Glacial Acetic Acid, 

Ether + Ligroin, 
Benzene + Ligroin. 

Less frequently used than these are : hydrochloric acid, carbon 
disulphide, acetone, chloroform, ethyl acetate, methyl alcohol, 
amyl alcohol, toluene, xylene, solvent naphtha, etc. 

But rarely used are : pyridine, naphthalene, phenol, nitro- 
benzene, aniline, and others. 

Choice of the Solvent. — The choice of a suitable solvent is 
often of great influence upon the success of an experiment, in that 
a solid compound does not assume a completely characteristic 
appearance until it is uniformly crystallised. In order to find the 
most appropriate solvent, preliminary experiments are made in 
the following manner : successive small portions of the finely 
pulverised substance (a few milligrammes will suffice) are treated 
in small test-tubes, with small quantities of the solvents of Class I. 
If solution takes place at the ordinary temperature, or on gentle 
heating, the solvent in question is, provisionally, left out of con- 
sideration. The remaining portions are heated to boiling, until, 
after the addition of more of the solvent if necessary, solution 



CRYSTALLISATION 3 

takes place. The tubes are now cooled by contact with cold 
water, and an observation will show in which tube crystals have 
separated in the largest quantity. At times crystallisation does 
not occur on mere cooling ; in this case the walls of the vessel 
are rubbed with a sharp-angled glass rod, or the solution is 
"seeded," i.e. a small crystal of the crude product is placed in the 
solution; by this means, crystallisation is frequently induced. If 
the individual solvents of Class I. are shown to be unsuitable, 
experiments are made with the mixtures, — Class II. Compounds 
which are easily soluble in alcohol or glacial acetic acid, and 
which consequently do not separate out on cooling, are, as a rule, 
difficultly soluble in water. In order to determine whether a 
separation of crystals will take place on cooling, the hot solutions 
in the pure solvents are treated with more or less water, according 
to the conditions. Substances easily soluble in ether, benzene, 
toluene, etc., often dissolve in ligroin with difficulty. Hence 
mixtures of these solvents can be frequently utilised with ad- 
vantage, in the manner just described. If these experiments have 
shown several solvents to be suitable, the portions under examina- 
tion are again heated until solution takes place, and this time 
are allowed to cool slowly. That solvent from which the best 
crystals separate in the largest quantity is selected for the crystal- 
lisation of the entire quantity of the substance. If a substance 
is easily soluble in all solvents, recourse must be had to crystallisa- 
tion by evaporation, i.e. by allowing the different solutions to stand 
some time in watch-glasses. That solvent from which crystals 
separate out first is the most suitable. Frequently a compound 
dissolves in a solvent only on heating and yet does not crystallise 
out again on cooling ; compounds of this class are said to be 
"sluggish" (trage). In this case, the solution may be allowed to 
stand for some time, if necessary over night, in a cool place. If 
a compound is very difficultly soluble, solvents with high boiling- 
points are used, as toluene, xylene, nitrobenzene, aniline, phenol, 
and others. The crystals obtained in these preliminary experi- 
ments, especially if they are of easily soluble substances, are pre- 
served, so that if from the main mass of the substance no crystals 



4 GENERAL PART 

can be obtained, the solution may be seeded, thus inducing 
crystallisation. The crystallisation of substances which boil with- 
out decomposition may often be facilitated by first subjecting them 
to distillation. 

To dissolve the Substance. — When water or glacial acetic acid, 
or a solvent which is not inflammable or not easily inflammable, is 
employed, the heating may be done in a beaker on a wire gauze 
over a free flame if the quantity is small ; if large, a flask is always 
used. In either case care must be taken to prevent the flask from 
breaking, by stirring up the crystals from the bottom with a glass 
rod, or by frequently shaking the vessel. This precaution is 
especially to be observed when, on heating, the substance to be 
dissolved melts at the bottom of the vessel. Alcohol and benzene 
may also be heated in like manner directly over a moderately 
large flame, if the student has already had a sufficient amount of 
experience in laboratory work and does not use too large quanti- 
ties. If the liquid becomes ignited, no attempt to extinguish the 
flame by blowing on it should be made, but the burner is removed 
and the vessel covered with a watch-glass, a glass plate, or a wet 
cloth. In working with large quantities of alcohol, benzene, ether, 
ligroi'n, carbon disulphide, or other substances with low boiling- 
points, they are heated on a water-bath in a flask provided with a 
vertical glass tube (air condenser) or a reflux condenser. A sub- 
stance to be crystallised from a solvent which is not miscible with 
water must be dried, in case it is moist, before dissolving. 

An error which even advanced students too often make in 
crystallising substances consists in this : an excessive quantity of 
the solvent is poured over the substance at once. When heat is 
applied, it is true, solution takes place easily, but on cooling noth- 
ing crystallises out. So much of the solvent has been taken that 
it holds the substance in solution even at ordinary temperatures. 
The result is that a portion of the solvent must be evaporated or 
distilled off, which involves a loss of time and substance, as well 
as decomposition of the substance. The following rule should, 
therefore, always be observed : The quantity of solvent taken at 
first should be insufficient to dissolve the substance completely, even 



CRYSTALLISATION 



5 



on heating; then more of the solvent is gradually added, until all oj 
the substance is just dissolved. In this way only is it certain that 
on cooling an abundant crystallisation will take place. If a mixt- 
ure of two solvents is used, one of which dissolves the substance 
easily and the other with difficulty, e.g. alcohol and water, the 
substance is first dissolved in the former with the aid of heat ; 
the heating is continued while small amounts of the second are 
gradually added (if water is used it is better to add it hot) until 
the first turbidity appearing does not vanish on further heating. 
In order to remove this cloudiness, a small quantity of the first 
solvent is added. On the addition of the first portions of the 
second liquid (water or ligroi'n) resinous impurities separate out 
at times ; in this case, these are filtered off before a further addi- 
tion of the solvent is made. 

At times it happens that the last portions of a compound will 
dissolve only with difficulty. The beginner often makes the mis- 
take here of adding more and more of the solvent to dissolve this 
last residue, which for the most part generally consists of difficultly 
soluble impurities, like inorganic salts, etc. The result of this is 
that on cooling nothing crystallises out. In such cases the diffi- 
cultly soluble portions may be allowed to remain undissolved, and 
on filtering the solution are retained by the filter. 

Filtration of the Solution. — When a substance has been dis- 
solved, the solution must next be filtered from the insoluble im- 
purities like by-products, filter-fibres, inorganic compounds, etc. 
For filtration a funnel with a very short stem is generally used, 
i.e. an ordinary funnel the stem of which has 
been cut off close to the conical portion (Fig. i). 
The funnels used in analytical operations have 
the disadvantage that when a hot solution of 
a compound flows through the stem, it be- 
comes cooled to such an extent that crystals 
frequently separate out, thus causing an obstruc- 
tion of the stem. The funnel with a shortened 
stem or no stem is prepared with a folded filter. In case the 
solution contains a substance that easily crystallises out, the filter 





6 GENERAL PART 

is made of rapid-filtering paper (Fig. 2). The solution to be 
filtered is not allowed to cool before filtering, but is poured on 
the filter immediately after removing it from the 
flame or water-bath. If inflammable solvents 
are used, care must be taken that the vapours 
are not ignited by a neighbouring flame. Under 
normal conditions, no crystals or only a few 
should separate out on the filter during filtra- 
tion. If large quantities of crystals appear in a 
solution as soon as it is poured on the filter, it is 
an indication that too small an amount of the solvent has been 
used. In a case of this kind, the point of the filter is pierced and 
the crystals are washed into the unfiltered portion of the solution 
with a fresh quantity of the solvent ; the solution is further diluted 
with the solvent, heated, and filtered. 

Very difficultly soluble compounds crystallise during the filtra- 
tion in the space between the filter and funnel, in consequence 
of the contact of the solution with the cold walls of the funnel. 

This may be prevented when a small quantity of liquid is to be 
filtered, by warming the funnel previously in an air-bath, or directly 
over a flame. If the quantity of the liquid is large, hot water or 
hot air funnels may be used (Figs. 3 and 4), or the funnel may 
be surrounded by a cone of lead tubing wound around it through 
which steam is passed (Fig. 5). Before filtering inflammable 
liquids, the flame with which the hot water or hot air funnel has 
been heated is extinguished. Substances which easily crystallise 
out again, may also be conveniently filtered with the aid of suc- 
tion and a funnel having a large filtering surface (Buchner funnel, 
see Fig. 38, p. 53). After filtration the solution is poured into the 
proper crystallisation vessel. In order to prevent the thick- walled 
filter-flasks from being cracked by solvents of a high boiling-point, 
they are somewhat warmed before filtering by immersion in warm 
water. 

Boiling nitrobenzene, aniline, phenol, and similar substances may 
be filtered in the usual way through ordinary filter-paper. 

Choice of the Crystallisation Vessel. — The size and form of the 



CRYSTALLISATION 7 

crystallisation vessel is not without influence upon the separation 
of the crystals. If a compound will crystallise out on simple cool- 
ing, without the necessity of evaporating a portion of the solvent, 
a beaker is used for the crystallisation. The shallow dishes known 
as " crystallising dishes " are not recommended for this purpose, 
since they cannot be heated over a free flame, and further, the 
solution easily " creeps " over the edge, involving a loss of the 
substance. Moreover, the crusts collecting on the edges are very 
impure, since, in consequence of the complete evaporation of the 
solvent, they contain all the impurities which should remain dis- 




Fig. 3. Fig. 4. Fig. 5. 

solved in the mother-liquor. The beaker is selected of such a 
size that the height of the solution placed in it is approximately 
equal to the diameter of the vessel, which is thus about one-half 
to two-thirds filled. 

Heating after Filtration. — Many compounds crystallise out in 
the beaker during filtration. The crystals thus obtained are never 
well formed, in consequence of the rapid separation ; therefore, 
after the entire solution has been filtered, it is heated again until 
the crystals have redissolved, and is then allowed to cool as slowly 



8 GENERAL PART 

as possible without being disturbed. In order to protect the 
solution from dust as well as to prevent it from cooling too rapidly, 
the vessel is covered first with a piece of filter-paper and then 
with a watch-glass or glass plate. The paper is used to prevent 
drops of the solvent formed by the vapours condensing on the cold 
cover-glass from falling into the solution, by which the crystallisa- 
tion would be disturbed. The paper need not be used if the 
vessel is covered with a watch-glass, the convex surface of which 
is uppermost : the condensed vapours will thus flow down the walls 
of the beaker. 

Crystallisation. — In order to obtain as good crystals as possible, 
the solution is allowed to cool slowly without being disturbed. In 
exceptional cases only is it placed in cold water to hasten the separa- 
tion of crystals. The vessel must not be touched until the crystalli- 
sation is ended. If a substance, on slow cooling, separates out in 
very coarse crystals, it is expedient, in case a sample of the substance 
for analysis is desired, to accelerate the crystallisation by artificial 
cooling, so that smaller crystals will separate out. Very coarse 
crystals are commonly more impure than smaller ones, in that they 
enclose portions of the mother-liquor. If a deposit of crystals as 
abundant as possible is desired, the vessel is put in a cool place — 
in a cellar or ice-chest if practicable. Should a compound crys- 
tallise sluggishly, the directions given on page 2, under " Choice of 
the Solvent," may be followed (rubbing the sides of the vessel with 
a glass rod; seeding the solution; allowing to stand over night). 
At times a compound separates out on cooling, not in crystals, but 
in a melted condition. This may be caused by the solution being 
so concentrated that crystallisation already takes place at a tem- 
perature above the fusing-point. In this case the solution is again 
heated until the oil which has separated out is dissolved, more of 
the solvent is then added, the quantity depending upon the condi- 
tions. In other cases this may be prevented by rubbing the walls 
of the vessel a short time with a sharp-edged glass rod, as soon as 
a slight turbidity shows itself, or by seeding the solution with a 
crystal of the same substance. This difficulty may also be avoided, 
in many cases, by allowing the solution to cool very slowly ; e.g. the 



CRYSTALLISATION 9 

beaker is placed in a larger vessel filled with hot water and allowed 
to cool in this. 

At times the separation of crystals takes place suddenly, within 
a few seconds, throughout the entire solution. Since the crystals 
thus obtained are generally not well formed, the liquid, after some 
of the crystals have been removed, is heated until solution again 
takes place. After it has partially cooled, those crystals which 
were taken out are now added to it, by which a gradual crystallisa- 
tion is caused. 

Separation of Crystals from the Mother-Liquor. — When crystals 
have been deposited, they are then to be separated from the liquid 
(mother-liquor). This is always done with the aid of suction, and 
never by merely pouring off the liquid. The filter to be used is 
previously moistened with the same substance which was employed 
as the solvent. Crusts, formed on the sides and edges of the ves- 
sel by the complete evaporation of the solvent, are not filtered 
with the crystals ; they are removed with a spatula before the filter- 
ing, and are worked up with the mother-liquor. In order to 
remove the last traces of the mother- liquor adhering to the crys- 
tals, they are washed several times with fresh portions of the solv- 
ent ; obviously, if the substance is easily soluble, too large quantities 
of the solvent must not be used. If a solvent that will not evap- 
orate easily in the air or on the water-bath has been used, e.g. 
glacial acetic acid, toluene, nitrobenzene, etc., it must be removed 
from the crystals by a more volatile substance, like alcohol or ether. 
This is done by first washing with a fresh quantity of the solvent, 
then with a mixture of the solvent and a small quantity of the more 
volatile liquid, the proportion of the latter in the washing mixture 
being gradually increased, until finally the volatile substance is 
used alone. Glacial acetic acid may, in this way, be displaced by 
water. 

Drying of Crystals. — When crystals have been freed from the 
mother-liquor they must be dried. This may be effected (1) at 
the ordinary temperature by the gradual evaporation of the solvent 
in the air, and (2) at higher temperatures by heating on a water- 
bath or in an air-bath. In the first case the crystals are spread 



IO GENERAL PART 

out in a thin layer upon several thicknesses of filter-paper and 
covered with a watch-glass, funnel, beaker, or similar vessel. In 
order that the vapours of the solvent may escape, the covering must 
be so placed that the air is not shut off completely from the crys- 
tals ; this is conveniently done by supporting it on several corks. 
Crystals may also be dried in a desiccator which is partially ex- 
hausted, if necessary. In drying substances at higher temperatures 
the crystal form may be lost by the fusion of the substance or by 
the separation of the water of crystallisation. Since many sub- 
stances will liquefy far below their melting-point if they contain 
even small quantities of the solvent, a preliminary experiment with 
a small portion is always made when the drying is to be effected 
at higher temperatures. Compounds, not easily soluble in ether, 
which crystallise from a solvent miscible with ether, can be very 
quickly dried by being washed several times with it. After a 
short exposure to the air they are dry. 

Treatment of the Mother-Liquor. — The mother-liquor filtered 
off from crystals still contains more or less of the substance, in 
proportion to its solubility at the ordinary temperature ; in many 
cases it is advantageous to extract the last portions remaining in 
solution. A "second crystallisation" is obtained by distilling or 
evaporating off a portion of the solvent. The mother-liquor may 
also be diluted with a second liquid, in which the dissolved sub- 
stance is difficultly soluble ; e.g. a solution in alcohol or glacial 
acetic acid may be diluted with water, or a solution in ether or 
benzene with ligroin. 

Crystallisation by Evaporation. — If a compound is so easily 
soluble in all solvents that it will only crystallise out on partial 
evaporation, then, in order to get good crystals, a solution, not 
too dilute, is made, by the aid of heat if necessary, and filtered 
from the impurities remaining undissolved. In this case, as a 
crystallisation vessel, one of the various forms of shallow dishes — 
the so-called crystallising dishes — is used, in which the solution 
is allowed partially to evaporate. In order to protect the vessel 
from dust, it is covered with a funnel or watch-glass, in the 
manner indicated under " Drying of Crystals." In crystallising 



CRYSTALLISATION 1 1 

by this method, it sometimes happens that the solution, owing to 
capillary action, will " creep " over the edge of the dish. To 
avoid loss of the substance from this source, the dish is placed on 
a watch-glass or glass plate. Under these conditions, the vessel 
is never covered with filter-paper, since, after standing some time, 
it may absorb the entire quantity of the substance. If, in order 
to obtain well- formed crystals, the solvent is to be evaporated as 
slowly as possible, the solution is placed in a beaker or test-tube, 
which is then covered with filter-paper. Evaporation may be 
hastened by placing the crystallisation vessel in a desiccator, 
charged, according to the nature of the solvent, with different 
substances ; for the absorption of water or alcohol, calcium chlor- 
ide or sulphuric acid is used; glacial acetic acid is absorbed by 
soda-lime, solid potassium hydroxide, or sodium hydroxide. The 
evaporation of all solvents may be hastened by exhausting the 
desiccator. 

Since the purifying effect of crystallisation depends upon the 
fact that the impurities remain dissolved in the mother-liquor, and 
with this are filtered off, in no case must the solvent be allowed 
to evaporate completely, but the crystals must be filtered off while 
still covered with the mother-liquor. Before filtering, crusts depos- 
ited, generally on the edges of the vessel, are removed with the 
aid of a small piece of filter-paper or a spatula. Even though 
the substance is very soluble, the mother-liquor adhering to the 
crystals is Washed away with small quantities of the solvent. If 
the quantity of crystals is very small, the adhering mother-liquor 
may be separated, in cases of necessity, by placing them on porous 
plates (biscuit or gypsum) and moistening with a spray of the 
solvent. 

Fractional Crystallisation. — Up to this point, it has been 
assumed that the substance to be crystallised possessed an essen- 
tially homogeneous nature, and the object of crystallisation was 
only to change it to a crystallised form. Crystallisation is often 
employed for another purpose — that of separating a mixture of 
different substances into its individual constituents, — a task that 
is generally far more difficult than the crystallisation of an individ- 



GENERAL PART 



ual substance. The simplest case is one in which two substances 
are to be separated. If the solubilities of the two substances are 
very different, as is generally the case when a mixture of two dif- 
ferent highly substituted compounds is under examination, it is 
frequently not difficult to find a solvent which will dissolve a con- 
siderable portion of the more easily soluble substance, and but a 
small portion of the less soluble. If, now, the mixture be treated 
with such a solvent, in not too large quantities, a solution will be 
obtained containing all of the easily soluble substance and a small 
portion of the difficultly soluble substance. 
This is filtered from the residue remaining 
undissolved. The mixture has thus been 
divided into two fractions. By evaporating 
the solution to a certain point, the more in- 
soluble compound will crystallise out, unac- 
companied by any of the other compound ; 
the crystals are filtered off, and the solution 
further evaporated. If the crystallisation of 
the two fractions be repeated a second time, 
a complete separation will be effected. For 
separating a mixture of this kind, specially 
constructed apparatus — the so-called ex- 
traction apparatus — may be employed, the 
use of which possesses the advantage over 
the method of simple heating, that much 
smaller quantities of the solvent are required. 
An apparatus of this kind is represented in 
Figs. 6 and 7. To a wide glass tube d is 
fused a narrow tube which acts as a siphon, 
bent as in Fig. 7. This portion of the 
apparatus is surrounded by a glass jacket b, 
narrowed at its lower end. This is con- 
nected with the flask that is to contain the 
solvent. A cork bearing a reflux condenser 
— a ball condenser is convenient — is fitted in the opening at the 
upper end of the jacket. A shell of filter-paper is next prepared 




Fig. 6. 



Fig. 7. 



CRYSTALLISATION 



13 



in the following manner : Three layers of filter-paper are rolled 
around a glass tube with half the diameter of the inner tube d. 
One end of the roll must extend somewhat beyond the edge of the 
glass tube ; this is turned over and securely fastened with thread. 
To preserve the form of the roll, thread is loosely wound around its 
middle and upper portion. The length of the roll is such that it 
extends 1 cm. above the highest point of the narrow siphon-tube. 
In the shell is placed the mixture of the easily soluble and diffi- 
cultly soluble substance to be extracted ; the upper end is closed 
by a loose plug of absorbent cotton. The flask a, containing the 
solvent, is now heated on a water-bath or over a free flame, accord- 
ing to the nature of the solvent. The condensed vapours drop from 
the condenser into the shell, dissolve the substance, filter through 
the paper, and fill the space between shell and inner glass tube. 
As soon as the liquid has reached the highest point of the siphon- 
tube, the solution siphons off and flows back into the flask a. 
This operation may be continued as long as necessary. The 
amount of solvent used should be one and a half or two times 
the volume of the inner tube up to the highest point of the siphon. 
The construction of a ball condenser is 
represented in Fig. 8. In order to dis- 
tinguish the tube by which the water en- 
ters from the outlet-tube, the former is 
marked with an arrow. Comparatively 
easy also is the separation of two sub- 
stances about equally soluble, if the one 
is present in larger quantity than the other. 
If a mixture of this kind is dissolved, then, 
on cooling, the substance which was pres- 
ent in larger quantity generally crystal- 
lises out. Occasionally, after standing 
some time, crystals of the second sub- 
stance will appear ; under these conditions the crystallisation 
must be carefully watched, and as soon as crystals differing 
from those first appearing are observed, the solution is filtered 
with suction at once, even though it is still warm. 




Fig. 8. 



14 GENERAL PART 

If two compounds crystallise simultaneously at the outset, as is 
the case when they possess approximately the same solubility and 
are present in almost equal quantities, they can be separated me- 
chanically. If, e.g., one of the compounds crystallises in coarse 
crystals, and the other in small ones, they may be separated by 
sifting through a suitable sieve or wire gauze. A compound crys- 
tallising in leaflets can frequently be separated from one crystal- 
lising in needles by a sieve. If these methods fail, the separation 
may be effected by picking out the crystals with small pincers or a 
quill. In all these mechanical operations, the crystals must be as 
dry as possible. 

In many cases, when one of the compounds is heavier than the 
other, it is possible to separate them by causing the lighter crystals 
to rise to the top of the liquid, by imparting to it a rotatory motion 
by rapid stirring with a glass rod. The heavier compound collects 
at the bottom of the vessel, and the liquid with the lighter com- 
pound floating in it can be poured off. 

Double Compounds with the Solvent. — Many substances crys- 
tallise from certain solvents in the form of double compounds, 
composed of the substance and the solvent. It is well known that 
many substances, in crystallising from water, combine with a cer- 
tain portion of water. Alcohol, acetone, chloroform, benzene, and 
others also have the power of uniting with other substances to 
form double compounds. As a familiar example, the combination 
of triphenylmethane with benzene may be mentioned in this con- 
nection. If double compounds of this kind are heated, the com- 
bined solvent is generally vaporised. 

SUBLIMATION 

Much less frequently than crystallisation, sublimation is used to 
purify a solid compound. The principle involved is this : A 
substance is converted by heat into the gaseous condition, and the 
vapours are caused to condense again on a cold surface. Under 
these 'conditions the substance frequently condenses in crystals. 

The sublimation of a small quantity of a substance can be con- 



SUBLIMATION 



15 



veniently effected between two watch-glasses of the same size. 
The substance to be sublimed is placed on the lower one, which is 
then covered with a round filter perforated several times in its 
centre and projecting over the edges ; the second watch-glass with 
its convex side uppermost is placed on it, and 
the two are held together by a watch-glass 
clamp. If the lower glass is now heated very 
slowly on a sand-bath with a free flame, the 
vaporised substance condenses on the cold sur- 
face of the upper watch-glass in crystals ; the 
filter-paper prevents the very small, light crys- 
tals from falling back on the hot surface of the 
lower glass. To keep the upper glass cool, it is 
covered with several layers of wet filter-paper 
or with a small piece of wet cloth. If large 
quantities of a substance are to be sublimed, 
the upper watch-glass in the apparatus just described is replaced 
by a funnel somewhat smaller than the lower glass (Fig. 9). To 
prevent the escape of vapours, the stem of the funnel is closed by 
a plug of cotton or is covered with a small cap of filter-paper. 
The apparatus for sublimation designed by Briihl is admirably 
adapted to the purpose for which it is intended (Fig. 10). It 
consists of a hollow metal plate through which water flows. In 




Fig. 9. 




Fig. 10. 



the conical opening is placed a crucible containing the substance 
to be sublimed. The plate is covered with a concave glass dish, 



1 6 GENERAL PART 

the ground edges of which fit the plate tightly. The crucible is 
heated directly with a small flame, while cold water flows through 
the plate. The vapours condense in part on the glass cover, but 
more abundantly on the upper cold surface of the plate in crystals. 
The glass cover is not removed until the apparatus is completely 
cold. 

Sublimations can also be conducted in crucibles, flasks, beakers, 
retorts, tubes, etc. The heating may be done in an air- or oil-bath. 
In order to lead off the vapours rapidly, a current of an indifferent 
gas is sent through the apparatus. 

DISTILLATION 

Kinds and Objects of Distillation. — By distillation is meant the 
conversion by heat of a solid or liquid substance into a vapour and 
the subsequent condensation of this. When distillation is con- 
ducted at the atmospheric pressure, it is called ordinary distilla- 
tion ; if in a partial vacuum, vacuum distillatioii. The object of 
distillation is either to test the purity of an individual substance 
by the determi?iation of its boiling-point, or to separate a mixture 
of substances boiling at different temperatures into its constituents. 
{Fractional Distillation.) 

Distillation Vessels. — The heating of the substance to be dis- 
tilled is generally effected in a fractionating flask (Figs, n, 12, 13). 
These flasks differ, not only in size, but in the diameter of the con- 
densation-tube (side-tube), as well as in the distance of the latter 
from the bulb. In selecting a fractionating flask the following points 
are to be observed. For distillation at the atmospheric pressure a 
flask is selected having a bulb of such a size that when it contains the 
substance to be distilled it will be about two-thirds filled. There 
are two objections to distilling small quantities of a substance from 
a large flask : the vapours are easily overheated, thus giving a 
boiling-point that is too high ; a loss of the substance follows, in 
that, after the distillation is finished, a larger volume of vapours 
which condense on cooling, remains behind in the bulb, than if a 
smaller flask had been used. In the distillation of low boiling 



DISTILLATION 



17 



compounds, a flask is selected which has its condensation-tube as 
high as possible above the bulb, so that the entire thread of mer- 
cury of the thermometer employed is heated by the vapour of the 
liquid. By using a flask of this kind it is not necessary to cor- 
rect the observed boiling-point, as is the case when the mercury 
column is not entirely surrounded by the vapour. The higher a 
substance boils, the nearer must the side-tube be to the bulb, in 




Fig. 11. 



Fig. 13. 



order that the vapours shall have as little opportunity as possible 
of condensing below the tube and flowing back into the bulb. 

If large quantities of a substance are to be distilled, an ordi- 
nary flask is used. This can be converted into a fractionating 
flask with the aid of a cork bearing a T-tube, as illustrated in 
Fig. 14. 

For the distillation of solid substances which solidify in the 
condensation-tube, a fractionating flask with a wide side-tube is 
used. 

A fractional distillation can also be conducted in the fractionating 
flasks just described ; but the operation can be carried out more 
c 



18 



GENERAL PART 



rapidly and more completely by the use of apparatus especially 
adapted to fractionating (Fig. 15). These can be fused directly 
on the bulb or they can be attached to an ordinary flask by means 
of a cork (Fig. 14) ; the round, short-necked flasks such as rep- 
resented in Fig. 16, are well adapted to this purpose. Flasks of 




Fig. 14. 



Fig. 15. 

Fractionating Apparatus. 

WURTZ LlNNEMANN HEMPEL 



this description can be obtained in different sizes but still possess- 
ing the same width of neck ; this enables one to use the same 
cork with any flask. The value of these different forms of fraction- 
ating apparatus depends upon the fact that the higher boiling 
portions carried along with the vapours do not pass immediately 



DISTILLATION 



19 



to the outlet tube, but before entering this they have an oppor- 
tunity of condensing and flowing back into the flask. In the 
apparatus of Wurtz (a) the condensation takes place on the large 
upper surfaces of the bulbs. More complete condensation is ob- 
tained in Linnemann's apparatus (3), which differs from that of 
Wurtz in that the narrow tubes between the bulbs contain small 
platinum-wire sieves. Since the lower 
boiling portions condense to a liquid 
and collect in these, the ascending 
vapours are so far cooled by the pas- 
sage through them that the accom- 
panying portions of the higher boiling 
substances are likewise condensed. 
The apparatus of Hempel is filled with 
glass beads which act like the sieves in 
the Linnemann apparatus. For the 
distillation of large quantities of a 
liquid the Hempel apparatus is par- 
ticularly well adapted ; in working with 
it as well as the Linnemann form, the 
heating must be interrupted from time 
to time, in order that the liquid col- 
lecting in the beads or sieves may have an opportunity to flow 
back to the distillation flask. If the Le Bel-Henninger form is 
used, this precaution is unnecessary, since in this apparatus 
special tubes for conducting off the condensed liquid are joined 
to the sides of the bulb somewhat above the sieves. 

Experiments have shown that a single distillation with one of the 
forms of apparatus just described, effects a more complete separa- 
tion than repeated fractionations in an ordinary fractionating flask. 

Supporting the Fractionating Flask. — If it is necessary to 
support the fractionating flask with a clamp, it is placed as far 
above the outlet tube as possible, never below it ; the glass ex- 
pands by contact with the hot vapours, and since the expansion 
is impeded by the clamp, particularly if it is firmly attached, the 
flask frequently breaks. 




Fig. 16. 



20 GENERAL PART 

Supporting the Thermometer. — The thermometer is passed 
through a cork (no rubber) which fits the neck of the flask. The 
most exact determinations of the boiling-point are obtained if the 
entire thread of mercury is surrounded by the vapour of the sub- 
stance. With low boiling compounds this condition is easily 
obtained by the use of a fractionating flask having its outlet tube 
at a sufficient distance above the bulb. In this case the ther- 
mometer is so placed that the degree corresponding to the boil- 
ing-point of the liquid is opposite the outlet tube, but the bulb 
of the thermometer must not extend into the bulb of the flask 
and never into the liquid ; if it does, another flask must be used, 
the outlet tube of which is still higher above the bulb. If in 
dealing with high boiling compounds such an arrangement is 
not possible, the thermometer is thrust so far into the neck of the 
flask that the thermometer-bulb is somewhat below the outlet 
tube. In this case, if an exact determination of the boiling-point 
is desired, the observed reading is corrected in the manner 
described below. In order to avoid making a correction a special 
form of thermometer is used, the graduation of the scale begin- 
ning at ioo°, 200°, or at other convenient points. By employing 
an instrument of this kind the mercury column may be kept in 
the vapours at any temperature. 

In making distillations, it occasionally happens that the mercury 
column ascends to that point in the scale which is hidden by the 
cork supporting the thermometer, thus preventing the temperature 
from being read. In a case of this kind the thermometer is 
either raised or lowered, so that the top of the mercury is visible, 
or if this is not possible, from that portion of the cork which pro- 
jects above the flask, a section is cut which will enable the scale 
to be seen. 

Condensation of Vapours. — The condensation of vapours is 
effected in various ways, depending upon the height of the boiling- 
point. If a compound boils at a relatively low temperature (up to 
ioo°), the outlet tube of the fractionating flask is connected with 
a Liebig condenser by a cork (not a rubber stopper). For very 
low boiling compounds a long condenser is used, and for those of 



DISTILLATION 



21 



high boiling-points a short one. If the boiling-point of a com- 
pound is very low, the flask in which the condensed liquid collects 
(the receiver) is connected with the condenser by means of a cork 
and a bent adapter (Fig. 63), and the receiver is cooled by ice 
or a freezing mixture. If the boiling-point is moderately high, 
between ioo° and 200 , the receiver, connected to the condensing 
tube by a cork, is cooled by running water (Fig. 17). If the 
substance is to be distilled 
again, a fractionating flask 
is employed as a receiver; a 
tubulated suction-flask may 
also be used. It is often 
unnecessary to employ run- 
ning water for cooling pur- 
poses if to the outlet tube of 
the flask a wide glass tube 
50 cm. long (extension tube) 
is connected by a cork (Fig. 
18). With still higher boil- 
ing substances even this is 
superfluous, since the con- 
densation tube of the frac- 
tionating flask, provided it 
is not too short, will suffice 
for the condensation. 

If a small quantity of a substance is to be distilled, and it is 
desired to avoid the loss of substance necessarily incident to the 
use of a condenser, the distillation even of low boiling compounds 
is conducted in a small distillation flask as slowly and carefully 
as possible, the source of heat being a minute flame (the so-called 
microburner). 

If large quantities are to be distilled, a condenser is always used, 
since when other condensation apparatus is employed, the tube 
finally becomes so hot that the vapours are not completely con- 
densed. If the vapours of a substance attack corks, the outlet 
tube is inserted far enough into the condenser or extension tube 




22 



GENERAL PART 



so that the vapours do not come in contact with the cork. But 
generally a cork is not used ; the outlet tube being inserted suffi- 
ciently far into the condenser. 

Heating. — Low boiling substances (those boiling up to about 
8o°) are not generally heated over the free flame, but on the water- 
bath gently or to full boiling. Frequently it is more convenient 
to immerse the bulb of the fractionating flask as far as the level 
of the liquid which it contains in a dish or beaker filled with 
water, which is heated gently or strongly as the case requires. 
Low boiling substances may also be heated by immersing the bulb 




Fig. 18. 



of the flask from time to time in a vessel filled with warm water. 
If a substance is not distilled over a free flame, in order to prevent 
" bumping " a few pieces of platinum wire or foil, or bits of glass, 
are thrown into the liquid (see below). When a substance to be 
distilled is heated on the water-bath, it may easily happen that 
the vapour inside the flask may be overheated by the steam escap- 
ing between the rings. For this reason, in the determination of 
exact boiling-points it is better to use a small free flame. The 
so-called microburner is well adapted to this purpose. High boil- 



DISTILLATION 23 

ing substances are always heated over the free flame. In this case 
the flask may be protected by heating it on a wire gauze ; still by 
working carefully the gauze need not be used. In heating, the 
flame is not placed under the flask at once, since the latter is likely 
to break easily on sudden heating ; it is better to pass the flame 
back and forth slowly and uniformly over the bottom of the flask 
until the liquid is brought to incipient ebullition. Substances which 
have been previously dissolved, after the evaporation of the solvent 
on the water-bath, often stubbornly refuse to give up the last por- 
tions of the solvent, particularly when ether has been used. If now 
a free flame be applied, it frequently happens that in consequence 
of a retarded boiling during which the solution becomes overheated, 
a sudden active ebullition and foaming will take place. In order 
to prevent this the flask is shaken repeatedly during the heating, 
since if the liquid is kept in motion, overheating cannot easily take 
place. It may also be prevented frequently by heating the flask 
on the side. During the actual distillation the heating may be con- 
tinued by slowly passing the flame over the bottom of the flask as in 
the preliminary heating, but in this case care must be taken not to 
apply the flame to the flask at any point above the liquid inside, 
since an overheating of the vapours would result. In order to 
protect the hand in case the flask should break, the burner is held 
obliquely and not directly under the flask ; or during the distilla- 
tion the burner may be placed under the flask and allowed to re- 
main stationary. The size of the flame is so regulated that the 
condensed distillate flows into the receiver regularly in drops. If 
vapours escape from the receiver, it is an indication that the heat- 
ing is too strong. Toward the end of the distillation the burner is 
turned down somewhat. 

To collect the Fractions. — If a substance which is not quite 
pure is being treated, and it is desired to test the purity by a 
determination of its boiling-point, then on distillation a small por- 
tion will generally pass over below the true boiling-point (" first 
runnings "); this is collected separately in a small receiver. Then 
follows the principal fraction, passing over at the true boiling-point, 
the temperature remaining constant. If there is only a small 



24 GENERAL PART 

quantity of the liquid in the bulb of the flask, it is difficult, in spite 
of using a small flame, to prevent the vapours from being some- 
what overheated ; this will cause a rise of the mercury The por- 
tion passing over a few degrees above the true boiling-point can, 
in preparation work, be collected with that portion which boils at 
the correct temperature, without evil results. High boiling portions 
collected separately are designated as "last runnings." The oper- 
ation of fractional distillation is conducted in a wholly different 
manner. The preparation of benzoyl chloride (see page 289) 
will furnish a practical example of the method of procedure. This 
compound is obtained by treating benzoic acid with phosphorus 
pentachloride. The product of the reaction is a mixture of phos- 
phorus oxychloride (b. p. no°) and benzoyl chloride (b. p. 200 ). 
If this mixture is subjected to distillation, the entire quantity of 
phosphorus oxychloride does not pass over at about no°, and 
afterwards the benzoyl chloride at 200 ; but the distillation will 
begin below no , and a mixture consisting of a large quantity of 
the lower boiling substance and a small quantity of the higher 
boiling substance will pass over ; the temperature then rises gradu- 
ally ; while the quantity of the former steadily decreases, that of 
the latter increases, until finally, at 200 , a mixture consisting essen- 
tially of the higher boiling substance passes over. A quantitative 
separation of the constituents of a mixture cannot be effected by 
the method of fractional distillation. However, in most cases, it 
is possible to obtain fractions which contain the largest part of 
the individual constituents, particularly when, as in the example 
selected, the boiling-points of the constituents lie far apart, by 
collecting the different fractions and repeating the distillation a 
number of times. It is almost impossible to give definite rules of 
general application for fractional distillation ; the number of frac- 
tions to be collected depends upon the difference of the boiling- 
points, upon the number of compounds to be separated, upon the 
relative proportion of the compounds present, and upon other 
factors. If but two substances are to be separated, as is generally 
the case in preparation work, the procedure is, very commonly, as 
follows : as a basis for the fractions to be collected, the interval 



DISTILLATION 25 

between the boiling-points is divided into three equal parts ; in the 
case of the example selected the temperatures would be i io°, 140 , 
170 , 200 . The fraction passing over between the temperature 
at which the distillation first begins, up to 140 , is collected (frac- 
tion I.), then in another vessel the fraction passing over between 
i4o°-i7o° (fraction II.), and finally in another receiver that pass- 
ing over between 170 and 200 (fraction III.). The quantities 
of the three fractions thus obtained are about equal. Fraction I. 
is now redistilled from a smaller flask, and the portion passing 
over up to 140 is collected as in the first distillation in the empty 
receiver I., which in the meantime has been washed and dried. 
When the temperature reaches 140 , the distillation is stopped, 
and to the residue remaining in the flask is added fraction II., and 
the distillation continued. The portion passing over up to 140 
is collected in receiver I., that from i4O -i7o° in the empty re- 
ceiver II. When the temperature reaches 170 , the distillation is 
again interrupted, and to the residue in the flask is added fraction 
III., and the distillation is again continued : in this way the three 
fractions are collected. These are again distilled as in the first 
distillation, but now the lower and higher boiling fractions are much 
larger than the intermediate one ; further, a larger portion of these 
end fractions boil nearer the true boiling-points than in the first 
distillation. If it is now desired to obtain the two substances in 
question in a still purer condition, the two end fractions are once 
more distilled separately, and the portion passing over a few de- 
grees above and below the true boiling-point, for phosphorus oxy- 
chloride about io5°-ii5°, for benzoyl chloride, i90°-205° are 
collected. 

Vacuum Distillation. — Many compounds, not volatile at the 
atmospheric pressure without decomposition, may be distilled 
undecomposed in a partial vacuum. The vacuum distillation is 
used advantageously for the fractionation of small quantities of a 
substance, since the separation of the individual constituents can 
be effected more rapidly and more completely than at the atmos 
pheric pressure. 

Vacuum Apparatus. — The simplest form of a vacuum apparatus 



26 



GENERAL PART 



is represented in Fig. 19. Two fractionating flasks a and b are 
connected by a cork. The neck of a is closed by a tightly fitting 
cork bearing the glass tube d, reaching to the bottom of the flask, 
its lower end being drawn out to a fine point, the object of which 
will be explained below. A thermometer is placed in the tube. 




a- — 



Fig. 19. 

In place of the flask b, a suction-flask such as finds application 
in filtering under pressure, may be used (Fig. 20). But this kind 
of flask is used only in case low boiling substances are to be 
distilled, since the contact of too hot liquids with the thick walls 
causes them to crack easily : this is likely to prove very destructive 
in vacuum distillation. With low boiling substances, in order to 
get complete condensation of the vapours, the jacket of a Liebig 
condenser through which water is allowed to flow is fitted over 
the outlet tube of the fractionating flask. These simple forms 
of apparatus are used only when it is desired to collect a few 
fractions, since it is troublesome to be obliged to change the 
receiver, and thus destroy the vacuum, for each new fraction. 
If it is desired to collect a larger number of fractions, an 



DISTILLATION 



27 



apparatus is employed by means of which the receiver can be 
changed without destroying the vacuum. 




Fig. 20. 



Briihl's apparatus is very well adapted to this purpose (Figs. 21 
and 22). By turning the axis b, so arranged that it supports the 
receivers firmly, each receiver may in turn be brought under the 
end of the condenser tube c. 

The receiver shown in Fig. 23 is also very convenient for frac- 
tional distillation in a vacuum. By grasping the cork a and the 
tube c firmly with the fingers and turning, the different portions 
of the receiver may be brought under the condensing tube. 

Construction of a Vacuum Apparatus. — In vacuum distillations 
the evolution of bubbles of vapour occurs to a much greater 
extent than under ordinary conditions. In order to prevent the 
liquid from foaming up and passing over, a flask of such a size is 
selected, that when it contains the liquid it must in no case be 
more than half full ; it is better to have it but one-third full. The 
individual parts of the apparatus are connected by rubber stoppers. 
Ordinary corks may also be used with almost equally good results, 
but only those are selected which are as free as possible from 



28 



GENERAL PART 



pores ; they are pressed in a cork-press, and then very carefully 
bored. If, after the apparatus is put together, the corks are coated 




Fig. 21. 

with a thin layer of collodion, there is no difficulty in obtaining a 
vacuum. The thermometer and capillary tube may be arranged as 

shown in Fig. 19. It is also 
a very excellent arrangement 
to use a two-hole cork, the 
thermometer passing through 
one, and the capillary tube 
through the other, as in Fig. 
21. The capillary tube is 
made by drawing out a glass 
tube of 1-2 mm. diameter ; 
the narrow hole in the cork 
through which this passes is 
made conveniently by a hot 
knitting-needle. Instead of 
using a capillary tube to 
prevent " bumping," other 




Fig. 22. 



DISTILLATION 



29 



means may be employed (see below), in which case the ther- 
mometer is supported in the fractionating flask as in ordinary 
distillations. When a tube drawn out to 
a capillary point is used, a short piece of 
thick-walled rubber tubing, which can be 
closed by a screw pinch-cock (Fig. 19, e 
and c), is attached to the upper end. 

The flasks recommended by Claisen 
(Fig. 24) may be used advantageously in 
vacuum distillations in place of the com- 
mon fractionating flasks. A tube drawn 
out to a capillary point is secured in the 
limb a by a piece of thick- walled rubber 
tubing or a cork. The thermometer is 
inserted in b. When a few large pieces of 
broken glass are placed in b, these flasks 
possess the advantage of preventing por- 
tions of the liquid (even in cases of violent 
boiling) from being carried over into the condenser. The space 
above the pieces of broken glass may be filled, partially or 




Fig. 23. 





Fig. 25. 



Fig. 24. 



wholly, with glass beads — obviously these are only to be used in 
the distillation of liquids not having a too high boiling-point — 



30 GENERAL PART 

thus combining the advantages of a Hempel column with vacuum 
distillation. 

For the distillation of solids a fractionating flask with a wide, 
bent sabre-shaped condensing tube is used (Fig. 25). In order 
to determine the efficiency of the vacuum, the lower tube of the 
Briihl apparatus is connected with a manometer (Fig. 26), by 
means of a thick-walled rubber tubing which will not collapse 
upon exhausting the apparatus. The other end 
of the manometer is connected with suction, by 
the same kind of rubber tubing. 

Since in consequence of the varying water 
pressure, it happens, at times, that the water from 
the suction pump may be forced into the man- 
ometer or receiver, it is advisable to insert a 
thick-walled suction flask between the suction 
pump and manometer. 

In order that the apparatus may be perfectly 
tight, the corks, ends of the rubber tubing, as well 
as the ground surfaces of the Briihl receiver, are 
covered with a thin layer of grease or vaseline. If ordinary corks 
are used, these, as well as the ends of the tubing, are covered 
with collodion after the apparatus is set up. Before the distil- 
lation, the apparatus is tested to determine whether it will give the 
desired vacuum. For this purpose, the pinch-cock on the capil- 
lary tube is closed, the suction attached, and after some time the 
manometer is read : this will indicate whether the desired vacuum 
has been obtained. In case it is not, the corks are pressed more 
firmly into the tubes, greased again or covered with more collodion, 
and the rubber tubing is pushed farther over the ends of the glass. 
Frequently the suction pump will not work satisfactorily ; it is 
then examined to see if it is stopped up, or a better pump is used. 
When the apparatus has been exhausted, the air must not be 
admitted suddenly, by removing a rubber joint, for the sudden 
rushing in of the air may easily destroy the apparatus. The 
rubber tube attached to the suction is closed by a screw pinch- 
cock which has been placed on it beforehand, and in case a 




DISTILLATION 3 1 

capillary tube has been used, the pinch-cock on this is gradually 
opened and the air allowed to enter through it, or after discon- 
necting the rubber tubing from the suction, the pinch-cock which 
has just been closed may be opened. The same object may be 
accomplished most rapidly by closing the tubing leading to the 
suction with the fingers, detaching it and opening the tube re- 
peatedly for an instant at a time, until the rushing sound made 
by the inflowing air ceases. After a test has shown that the 
apparatus does not leak, the liquid to be distilled is poured in 
the flask and the distillation begun. 

Heating. — In vacuum distillation the flask can be heated 
directly with a free flame, but the flame must be applied to- the 
side, and not to the bottom of it, as in the ordinary way. Care 
must be taken to keep the flame constantly moving. It is much 
more satisfactory and safer to use an oil- or paraffin-bath, or better 
a metallic air-bath (iron crucible). The latter is covered with 
a thick asbestos plate containing a round opening in the centre, 
through which the neck of the fractionating flask may pass ; from 
the opening to the edge of the plate there is a straight narrow slit. 
The air-bath must not be too large ; the bottom is covered with 
a thin layer of asbestos, which will prevent the flask from coming 
in contact with the metal. The temperature of the oil- or air- 
bath should, in exact experiments, not be more than 20°-30° 
higher than the boiling-point indicated by the thermometer. A 
thermometer is immersed in the bath and the flame so regulated 
that the difference between the two thermometers is not greater 
than that mentioned. The heating is not begun until the appara- 
tus is exhausted. 

To prevent Bumping. — In vacuum distillations a troublesome 
bumping (a sudden, violent ebullition) frequently occurs. To pre- 
vent this a slow, continuous current of air is drawn through the 
liquid, thus keeping it in constant motion. The air current, con- 
trolled by a pinch-cock, must not be allowed to enter too rapidly, 
otherwise it will be difficult to maintain a high vacuum. The 
same effect may be obtained by placing certain substances in the 
liquid — splinters of wood the size of a match, capillary tubes, bits 
of glass, pieces of porcelain, powdered talc, scraps of platinum 
wire or foil. Small pieces of pumice-stone bound with platinum 



32 



GENERAL PART 



wire also act satisfactorily. For further details concerning vacuum 
distillation consult " Die Destination unter vermindertem Druck 
im Laboratorium," R. Anschiitz. 

Lowering of the* Boiling-Point. — In order that some idea may 
be obtained as to the approximate lowering of the boiling-point, 
by diminishing the pressure, the following table is given : 



Substance. 


Boiling-point at 
12 mm. 


Boiling-point at 
Ordinary Pressure. 


Difference. 


Acetic acid 

Monochloracetic acri . . 

Chlorbenzene 

p-Nitrotoluene .... 
Acetanilide 


19° 

84 

2 7 ° 

io8° 
1 67 


n8° 
1 86° 
132 
236 

295° 


99° 

102° 
IO5 
1 28° 

128° 



Corrections of the Boiling-Point. — If it is not possible in 
making an exact determination of the boiling-point to have the 
mercurial column entirely surrounded by the vapour of the liquid, 
— a condition usually obtained by employing a flask, the side-tube 
of which is at a sufficient distance from the bulb, or a sectional 
thermometer, or both, — then a correction may be applied to the 
observed boiling-point in one of two ways. The portion of the 
mercurial column not heated by the vapours — that portion above 
the side-tube — is read in degrees (Z). Another thermometer 
is brought as near as possible to the middle point of this col- 
umn, the temperature of which is also read (/). If T is the 
observed boiling temperature, then the following correction is 
added : L{T—f) • 0.000154. The so-called " corrected " boiling- 
point may also be obtained as follows : The boiling-point is 
determined in the usual way ; after the distillation, another sub- 
stance, the corrected boiling-point of which is known, and which 
lies near the one in question, is placed in the same flask and dis- 
tilled under the same conditions. The difference between the 
corrected and observed boiling-points is applied to the boiling- 
point of the first substance. 

Distilling off a Solvent. — An operation frequently employed 
in organic work is distilling off a solvent from the substance dis- 



DISTILLATION 33 

solved in it. When the boiling-point of the solvent is sufficiently 
far away from that of the dissolved substance, a complete separa- 
tion can be effected by a single distillation. The methods used 
depend upon the quantity of the solution, that of the dissolved 
substance and the boiling-point of the solvent. The methods 
which can be used for distilling off low boiling solvents, like ether, 
ligroin, carbon disulphide, alcohol, and others, will be described 
first. If a small quantity of a solvent is to be evaporated, and it 
is not worth the trouble to recover it by condensation, then, in 
case the solvent is ether, ligroin, or carbon disulphide, the solution 
is poured into a small flask, and this is immersed in a larger vessel 
filled with warm water. The vaporisation is considerably accel- 
erated by shaking the flask. The operation is more rapidly per- 
formed by heating the flask on a water-bath. To prevent a 
sudden foaming, due to retarded ebullition, some small pieces of 
platinum wire or capillary tubes are placed in the liquid ; the 
evaporation is also facilitated by frequent shaking. Should the 
vapours become ignited from the flame of the water-bath, no 
attempt to blow out the burning vapours should be made; but 
the burner is extinguished, the flask removed from the bath with 
a cloth, and the mouth covered with a watch-glass. Carbon disul- 
phide, on account of its great inflammability, is never vaporised 
in this way, but always without a flame. 

Large quantities of solvents may also be evaporated by these 
two methods, but the entire quantity is not treated at once. A 
portion is placed in a small flask, and when this has been evap- 
orated, a second portion is added, and so on. The danger of 
ignition of the solvent may be avoided by inserting in the flask 
a glass tube, extending to within a few centimetres of the level 
of the liquid, supported firmly by a clamp, and attached by rubber 
tubing to the suction. The tube must at no time touch the 
liquid. 

For rapid evaporation of small quantities of ether, the following 
method of procedure is recommended : A few cubic centimetres 
of the solution are placed in a sufficiently wide test-tube ; this is 
warmed, with continuous shaking, over a small, luminous flame. 



34 



GENERAL PART 



After the first portion is evaporated, the second is added, and 
so on. Since the vapours of the ether almost regularly become 
ignited, this event should always be expected, and should occasion 
no alarm. When it happens, the heating is interrupted for a 
moment, and the flame is easily extinguished by blowing on it or 
covering the mouth of the test-tube. If the tube is held as nearly 
horizontal as possible during the heating, the danger of ignition 
is lessened. 

If it is desired to distil off a larger quantity of ether, ligro'in, 
or carbon disulphide, and to recover it by condensation, the re- 
ceiver is attached to the condenser tube by a cork, and the flask 
is heated by immersing it in a water-bath containing hot water. 
To prevent the liquid from being superheated, a silk thread as 
frayed as possible at the end reaching to the bottom of the flask 
is suspended from the neck and the flask is shaken frequently 
during the distillation (Fig. 28). The entire quantity of the liquid 
is not placed in the flask at once, but only a portion : after the 
solvent has been distilled off from this, an- 
other portion is added, and so on. 

By the use of the so-called safety water- 
bath, i.e. one in which the flame is sur- 
rounded by a wire gauze as in Davy's Safety 
Lamp, ether and ligroin can be distilled by 
continuous heating with a flame. It is not 
safe to distil off carbon disulphide even from 
this apparatus, since, when it becomes suffi- 
ciently hot, it will ignite spontaneously with- 
out the intervention of a flame. 

By the use of a coil condenser (Fig. 
27) the distillation of solvents is greatly 
facilitated. The free flame, if it be sur- 
rounded by a cylinder of wire gauze, may 
be employed in place of a water-bath. 
A piece of rubber tubing attached to the 
side tube of the receiver carries the vapours to a hood or below 
the surface of the table. 




Fig. 27. 



DISTILLATION 



35 



The apparatus best adapted to distilling off any desired quan- 
tity of ether is represented in Fig. 29. A fractionating flask, 
into the neck of which a dropping- funnel is inserted, is con- 
nected with an ordinary condenser or an upright coil condenser. 
During the heating by means of hot water, or in special cases, 
the water-bath may be heated with a flame, or the flask may be 
heated directly by a flame protected by a safety gauze, the ethereal 
solution is allowed to flow gradually from the dropping- funnel into 
the flask in the bottom of which are a few scraps of platinum. 




Fig. 28. 



If the flow of the solution is regulated so that the same quantity 
of liquid is added as that distilled, the operation may be carried 
on continuously for hours. The quantity of ether collected in the 
receiver is prevented from becoming too large, by pouring it into a 
larger vessel from time to time. To protect the ether from igni- 
tion, the mouth of the receiver is closed by a loose plug of cotton, 
or the receiver, united to the condensing tube by a cork, is con- 
nected with the hood by rubber tubing. Besides its convenient 
manipulation, this method possesses the further advantage that 
after the completion of the distillation the dropping-funnel may 
be replaced by a thermometer, and the residue can be distilled 
directly from the fractionating flask. This is an especially eco- 



36 



GENERAL PART 



nomical procedure when the quantity of the dissolved substance 
is small. In a case of this kind the size of the flask is selected 
with reference to the residue that may be expected. In distilling 
off alcohol, it is necessary to heat the water-bath continuously, 
and to always use threads. The distillation may be hastened by 
placing the flask not upon, but in, the water-bath. If a solution 
of common salt is employed in the bath, the temperature is raised, 
and the distillation proceeds still more rapidly. 

If one has had sufficient experience in laboratory work, alcohol 




Fig. 29. 



may be distilled off by heating the flask on a wire gauze or sand- 
bath over a flame. In this case especial care must be taken not 
to use too large quantities at one time. Benzene can be distilled 
off under the same conditions as alcohol. The methods appli- 
cable to high boiling liquids have been given under " Distilla- 
tion." (See page 16.) 

In comparatively few cases the difference between the boiling- 
points of the solvent and the dissolved substance is a slight one ; 
under these conditions the separation must be effected by a 
systematic fractional distillation with the aid of fractionating 
apparatus. 



DISTILLATION WITH STEAM 37 



DISTILLATION WITH STEAM 

A particular kind of distillation, very frequently employed in 
organic work for the purification or separation of a mixture, is dis- 
tillation with steam. Many substances, even those distilling far 
above ioo°, or those not volatile without decomposition, possess 
the property, when heated with water, or when steam is passed 
over or through them, of volatilising with the steam. This phe- 
nomenon finds its explanation in the fact that the atmospheric 
pressure acting upon the mixture is naturally divided between the 
steam and the other substance, so that the partial pressure upon 
the latter is accordingly less than the atmospheric pressure, in 
consequence the volatility is increased. The distillation with 
steam is therefore to be regarded as a special case of distillation 
in a partial vacuum. 

Apparatus. — The apparatus used for distillation with steam 
is represented in Fig. 30. A round flask inclined at an angle 
is closed by a two-hole cork ; through one hole passes a not 
too narrow glass tube reaching to the bottom and serving to 
lead in the steam ; the other hole bears a short glass tube 
the end of which is just below the cork, the other end is con- 
nected with a long condenser. The distillation flask selected is 
of such a size that the liquid fills it not more than half full. 
In order that the steam may act on an oil at the bottom of 
the flask, the inlet tube is bent so that it may reach the lowest 
point of the flask. Steam is generated in a tin vessel about 
half-filled with water, the neck being closed by a two-hole stop- 
per ; into one hole is inserted a safety-tube partially filled with 
mercury ; the lower end of this tube does not touch the water ; 
through the other hole passes the outlet tube bent at a right 
angle. 

Method of Procedure. — The experiment is begun by heating 
the steam generator and the flask simultaneously, the former con- 
veniently by means of a low burner (Fletcher burner). The flask 
may be heated on a wire gauze over a free flame ; but since at 



38 GENERAL PART 

times a very troublesome "bumping" will occur, it is better, if 
this happens, to heat on a briskly boiling water-bath. As soon 
as the water in the generator boils and the liquid in the flask has 
been heated to the proper point, the tubes of the two vessels are 
connected with rubber tubing. The distillation is then continued 
until the condensed steam passes over unaccompanied by any of 
the substance. Should the steam escape from the safety-tube, 
the generator is being heated too strongly, and the flame should 
be lowered. To prevent the partial condensation of vapours in 
the upper cool part of the flask this should be covered with sev- 
eral layers of thick cloth to lessen the radiation of heat. If the 
quantity of substance to be distilled is small, so that only a small 
flask need be used, the preliminary and continued heating of the 
latter is superfluous : the steam can be passed at once into the 
cold liquid. If a compound is very easily volatile with steam, 
the introduction of the latter may be omitted ; in this case it is 
only necessary to mix the compound with several times its volume 
of water and distil directly from the flask. If the substance to 
be distilled is solid, and its vapour forms crystals in the condenser, 
these may be removed provided the substance melts below ioo°, 
by drawing off the water in the condenser for a short time. The 
substance is melted by the hot steam and flows into the receiver. 
If after this operation the water is to be turned into the condenser 
again, it must be done slowly at first, otherwise the cold water 
coming in contact with the hot condenser may easily crack it. 
When the melting-point of the substance is above ioo°, in order 
to keep the condenser free from crystals, the distillation is inter- 
rupted for a short time, and the crystals are pushed out of the 
tube by a long glass rod. 

The end of the operation is indicated, if the substance is diffi- 
cultly soluble in water, by the fact that the water passing over 
carries no drops of oil or crystals with it. But when the substance 
is soluble, even though the condensed water is apparently pure, it 
may still contain considerable quantities of the dissolved substance. 
In this case, to determine when the end of the operation has been 
reached, a small quantity, about 10 c.c, is collected in a test-tube, 



DISTILLATION WITH STEAM 



39 




40 GENERAL PART 

shaken up with ether, the ether decanted and evaporated. If no 
residue remains, the distillation is finished. When a substance 
shows a colour reaction, e.g. aniline with bleaching powder, 
advantage is taken of this to decide the question. After the 
distillation is ended the rubber tubing is first removed from the 
distilling flask, and then, after this has been done, the flame under 
the generator is extinguished. This point is also carefully ob- 
served when the distillation is interrupted ; otherwise it may 
happen that the contents of the flask will be drawn back into 
the generator. 

Superheated Steam. — In dealing with very difficultly volatile 
compounds, it is frequently necessary to conduct the distillation 
with the aid of superheated steam. A conically wound copper 
tube is interposed between the steam generator and the distilling 




Fig. 31. 

flask (Fig. 31). In order to superheat the steam, a large burner is 
placed under the spiral in such a position that the flame comes in 
contact with the interior of the spiral. Since for many purposes 
it is necessary to use superheated steam at a definite temperature, 
a small opening is made in the steam exit and a piece of metal 
tubing affixed to it. A thermometer is inserted into this tubulure 
and held in position by means of asbestos twine. The distillation 
is still further facilitated by heating the flask to a high tempera- 
ture in an oil- or water-bath. Under these conditions the sub- 
stance to be distilled is not covered with a layer of water. 



SEPARATION OF LIQUID MIXTURES 



41 



SEPARATION OF LIQUID MIXTURES. SEPARATION 
BY EXTRACTION. SALTING OUT 





Separation of Liquids. — If the separation of large quantities of 
two non-miscible liquids, one of which is for the most part water 
or a water solution, is to be effected, it can be done 
with a separating funnel (Fig. 32). If the liquid 
desired is of a greater specific gravity than that of 
water, it is allowed to flow off through the stem by 
opening the cock. If, however, it floats upon the 
water, the latter is first allowed to flow off, and the 
liquid remaining is poured out of the top of the fun- 
nel. By this manipulation the liquid is prevented 
from coming in contact with the portion of water 
remaining in the cock, and adhering to the sides of 
the stem. For the separation of small quantities of 
liquids a small separating funnel, the so-called drop- 
ping funnel, is employed. If the quantity of liquid is 
so small that even a dropping funnel is too large, a 
capillary pipette is used (Figs. $Z an d 34). The mixture to be 
separated is placed in a narrow test-tube, the pipette is immersed 
in the mixture almost to the surface of contact of the two liquids 
in case the upper layer is to be removed, the test-tube is brought 
to the level of the eyes, and the upper layer drawn off. The 
tubing is then closed by pressure with the teeth or fingers and the 
pipette removed from the tube. If the lower layer is the one 
desired, the pipette is immersed to the bottom of the test-tube, 
and the operation conducted as before. Pipettes of this kind are 
very easily made from glass tubing ; and if one is accustomed to 
work with them, are indispensable. 

Separation by Extraction. — When a substance is held in sus- 
pension or dissolved in a liquid, generally water, the removal of 
the dissolved substance may be effected by agitating the solution 
with another solvent which will more readily dissolve the substance, 
but which is not miscible with the first liquid, drawing off this and 



42 



GENERAL PART 



distilling it. For extraction, ether is generally used; in special 
cases carbon disulphide, ligroin, chloroform, benzene, amyl alco- 
hol, etc., may be used. In the discussion following it will be 
assumed that the extraction is made with ether. 

If the liquid to be separated is insoluble in water and is present 
in such a small quantity that a direct separation would cause a 
loss owing to the adhesion of the liquid to the walls of the vessel, 
or if it is held in suspension by the water in the form of individual 





^\ 



Fig. 33. 



Fig. 34- 



drops, ether is added to the mixture; it is then shaken, allowed 
to stand, the two layers separated, and the ether evaporated. 

A similar method is followed if the substance is completely 
soluble in water, or if a portion of it is soluble and the 
remainder held in suspension. If from an aqueous solution a 
considerable portion of a solid or liquid separates out, it is not 
immediately extracted with ether, but if the substance sepa- 
rating out is a solid, it is first filtered off; if a liquid, the oily 
layer is separated in a dropping funnel, and then the filtrate is 



SEPARATION BY EXTRACTION 43 

extracted with ether. In many cases, e.g. when the layer of oil 
is very turbid, or the solution strongly acid or alkaline, thus 
rendering filtration difficult, the entire solution may be treated 
at once with ether. With substances soluble in water the extrac- 
tion must be repeated one or more times in proportion to the 
greater or less solubility of the substance. If it is desirable to avoid 
using large quantities of ether, after the first extraction it is dis- 
tilled off and used for the second extraction, and so on. The 
extraction is repeated until a test portion of the ethereal solution, 
evaporated on a watch-glass, leaves no residue. If the test portion 
is evaporated by blowing the breath on it, the beginner will prob- 
ably often be deceived by the appearance of an abundant quan- 
tity of crystals of ice, formed by the condensation of the moisture 
of the breath, due to the cold produced by the evaporation of the 
ether. Another error into which the beginner often falls when 
extracting with ether is this : in most chemical processes small 
quantities of coloured impurities are formed ; on extraction, these 
impart a colour to the ether. The tendency is to continue the ex- 
traction until the ether is no longer coloured; but the proper method 
of procedure is just the reverse of this. On extracting colourless 
compounds, the colouring of the ether does not show that it still 
contains any of the substance dissolved ; the above-mentioned test 
gives the only safe indication of the presence of the substance. 

In an extraction the following points are to be observed : Hot 
liquids are allowed to stand until they are cold before they are ex- 
tracted with ether, carbon disulphide, or other low boiling solvents. 
It frequently happens that, after long standing, two layers of liquids 
will not separate, in consequence of the formation of a flocculent 
precipitate floating in the liquids at the surface of contact. This 
difficulty may be obviated either by stirring the liquids with a glass 
rod, or by giving the separating funnel a circular motion in a hori- 
zontal plane, in such a way as not to cause the two layers to be 
mixed by the shaking. Under certain conditions the neck of the 
funnel may be closed with a cork bearing a glass tube attached to 
the suction ; by this means the space over the liquid is exhausted. 
The bubbles of gas which now rise through the liquid frequently 



44 GENERAL PART 

destroy the troublesome emulsion. The same object may also be 
attained by adding a few drops of alcohol to the ether. If the sepa- 
ration of the layers is very imperfect, the cause is often due to the 
fact that an insufficient quantity of ether has been used ; in this case 
more ether is added. If all of these methods prove ineffectual, then 
a complete separation may be obtained by first filtering the mix- 
ture, best with the aid of a Biichner funnel, which will retain the 
precipitate causing the emulsion, and then allowing it to stand. 

Occasionally when extracting an aqueous solution containing 
inorganic salts with ether, they will separate out as solids. In 
this case water is added until the salts are redissolved, or the 
solution is filtered, with suction. 

If the specific gravity of an ethereal solution is approximately the 
same as that of the water solution, the separation often takes place 
only with difficulty. Some common salt is then added, by which 
the specific gravity of the aqueous solution is increased. 

Under certain conditions both the ethereal and aqueous solu- 
tions are so coloured that they cannot be distinguished. In this 
case the separating funnel is held toward the light ; in the even- 
ing a luminous flame is placed behind it, and the eye is directed 
to the liquid at a point just above the cock. On opening the 
cock, the eye will readily detect the layer separating the two 
liquids, as it approaches the opening. 

Salting Out. — A very valuable method to induce substances 
dissolved in water to separate out is known as " salting out." 
Many substances soluble in pure water are insoluble or difficultly 
soluble in an aqueous solution of certain salts ; if, therefore, sodium 
chloride, potassium chloride, potash, calcium chloride, ammonium 
chloride, Glauber's salt, sodium acetate, ammonium sulphate, or 
other salt is added to the solution, this is dissolved, and the sub- 
stance previously in solution separates out. By this method many 
compounds like alcohol, acetone, etc., which are so easily soluble 
in water that they cannot be removed from it by extraction with 
ether, can be separated out with ease. The method of procedure 
is this : One of the above-mentioned salts, usually solid potash, is 
added to the solution until no more will dissolve. The substance 



DECOLOURISING. REMOVAL OF TARRY MATTER 45 

thus forced out of solution collects above the heavier salt-solution 
and is removed by decantation or suction. 

A combination of extraction and salting out also presents many 
advantages. If to the solution of a compound in water one of 
the salts mentioned is added — it is best to use finely pulverised 
sodium chloride — before the extraction with ether, this latter is 
greatly facilitated for several reasons. In the first place, a portion 
of the dissolved substance will separate out, due to the " salting 
out " action ; furthermore, the solubility of the substance in the 
the new solvent — sodium chloride solution — will be diminished 
so that on extracting, a larger portion is dissolved by the ether 
than on treating the solution directly with it, and finally, ether 
does not dissolve so readily in a sodium chloride solution as in 
water, so that the volume of the ethereal solution is larger. The 
amount of sodium chloride to be added is about 25-30 grammes 
of the finely pulverised salt to 100 c.c. of the aqueous solution. 
Unfortunately the method of "salting out" has not been so 
generally adopted in scientific laboratories as it deserves, while in 
the laboratories of technical chemists it has long been in daily 
use. Among the reagents constantly used, a bottle of solid sodium 
chloride should not be wanting. In many cases, instead of the 
salt, a concentrated aqueous solution may also be used. 

DECOLOURISING. REMOVAL OF TARRY MATTER 

As is well known, animal charcoal possesses the property of 
being able to remove the colour from certain solutions ; for this 
reason it is frequently employed in the laboratory to free a colour- 
less substance from coloured impurities. If it is to be used to 
remove the colour of a solid substance, the latter is first dissolved 
in a suitable solvent, then boiled with the animal charcoal and 
filtered. Before treating a hot solution, it is allowed to cool 
somewhat, since when animal charcoal comes in contact with 
liquids heated nearly to the boiling-point, a violent ebullition is 
frequently caused, and an overflowing of the liquid may easily take 
place. When a solvent not miscible with water is used, the ani- 



4 6 GENERAL PART 

mal charcoal, which is generally moist, is previously dried on the 
water-bath. The solvent selected is such that upon cooling the 
decolourised solution, the substance will crystallise out. In carry- 
ing out this operation, the general rule that no animal charcoal is 
added until the substance to be decolourised has completely dis- 
solved, should be followed. Under these conditions only, is it 
certain that a portion of the substance does not remain undissolved 
mixed with the charcoal. The quantity of animal charcoal to be 
added to a solution depends upon the intensity of the colour of 
the latter. To a solution very slightly coloured, a small quantity 
is added ; to a deeply coloured solution, a larger quantity. Very 
finely divided precipitates in water which pass through the filter 
may also be removed by the use of animal charcoal. When, e.g. 
tin is precipitated with hydrogen sulphide, the tin sulphide is 
often so finely divided that it runs through the filter. If the 
liquid is boiled with animal charcoal, the filtration presents no 
difficulty. 

The use of animal charcoal, especially when it is in a very finely 
divided condition, has the disadvantage that at times it passes 
through the filter and contaminates the filtrate. This may be 
prevented frequently, by filtering again, or by boiling the filtrate 
a few minutes before the second filtration. When substances to 
be analysed have been decolourised with animal charcoal, care 
must always be taken to prevent the contamination of the sub- 
stance. In such cases it is again crystallised without the use of 
animal charcoal. This difficulty may also be prevented or essen- 
tially lessened, by washing the charcoal with water several times 
before using ; the portion suspended in the water is decanted, and 
only the coarser residue which easily settles at the bottom is used. 

Recently the use of animal charcoal in the sugar industry has 
been replaced in part by a mixture of fine wood meal and floated 
infusorial earth (kieselguhr). This mixture ought to be of great 
advantage in the laboratory, for decolourising purposes, if used in 
the same way on a small scale. To the mixture is ascribed very 
superior purifying properties, so that by using much smaller quan- 
tities the same effect is obtained as with far larger quantities of 



DRYING 47 

animal charcoal. In order to prevent an easily oxidisable liquid 
from decomposing when it is heated in the air — this action being 
generally attended with more or less colouration — a gaseous re- 
ducing or protecting agent is passed through it ; e.g. sulphur dioxide, 
hydrogen sulphide, or carbon dioxide. Very easily oxidisable sub- 
stances are not evaporated in a dish, but in a flask, since in this 
the liquid is better protected from the action of the air. 

Not only coloured impurities, but those of a tarry character, 
may also be removed by boiling with animal charcoal as above 
described. A mixture of wood meal and infusorial earth with 
which the solution may likewise be boiled is said to be of great 
value. 

For the absorption of tarry impurities, in so far as they are 
liquid or oily, unglazed, porous plates (drying plates) may be 
used with advantage, the substances being firmly pressed out with 
a spatula in a thin layer. If one pressing out is insufficient, the 
substance is spread out again upon a fresh, unused portion of 
the plate. The absorption of an oil may often be facilitated by 
moistening the substance on the plate with alcohol, ether, or 
ligroi'n, which at times will dissolve the impurities without causing 
a solution of the substance. Oily by-products may also be removed 
by pressing the substance between a number of layers of filter- 
paper. For this purpose either a screw-press is used, or the 
substance is placed in layers of filter-paper between two wooden 
blocks, the upper one of which bears a heavy object. 

DRYING 

Drying Solid Compounds. — Under the chapter on "Crystallisa- 
tion," page 9, the method of drying moist crystals has already been 
given. This method is naturally applicable to all solids, even if 
they are not crystallised, or only imperfectly crystallised, so that it 
will be unnecessary to repeat the directions already given. But 
a few methods, not so refined, and generally employed in dealing 
with crude products will be referred to here. Before a substance 
is dried by allowing it to lie in the air or in a desiccator, or by 



48 GENERAL PART 

heating, the greatest portion of the moisture is removed by press- 
ure, as follows : The substance lying between a number of layers 
of filter-paper is placed in a screw press, and pressure applied. 
The operation is repeated, and the paper renewed, until it is no 
longer moistened. If a solid is not contaminated by water or other 
solvent, but by a liquid by-product, which one desires to obtain, 
the paper, after it has absorbed this liquid substance, can be ex- 
tracted with a solvent, like ether. Large masses of a compound 
not too finely granulated can be tied up in a piece of filter- cloth 
of fine texture, placed in the screw press, and pressure applied. 
Smaller quantities of a substance may be pressed out between two 
wooden blocks, the upper of which bears a heavy object. Generally 
one places the blocks on the floor and stands on them. 

Very often solids may be dried by making use of the power 
of unglazed porcelain to absorb liquids with avidity. The sub- 
stance to be dried is pressed out in a thin layer upon a suitable 
piece of an unglazed porcelain plate, with a spatula, and is allowed 
to stand for some time, longer or shorter, as may be necessary. 
If one pressing out is not sufficient, the operation is repeated, 
using a fresh plate. Oily and tarry impurities may also be removed 
in this way, as mentioned above. 

Compounds which fuse without decomposition may be dried 
either upon the water-bath or in an air-bath, or by heating over 
a free flame until they melt, allowing them to solidify, and then 
pouring off the water. 

In order to dry a substance at a high temperature in a vacuum, 
two glass hemispheres, the edges of which are ground and fitted 
together, are used. The upper vessel is supplied with a tubulure, 
the opening of which is closed by a cork bearing a glass tube bent 
at a right angle connected with suction. The sphere may be 
heated by immersion in a large quantity of hot water or on a 
boiling water-bath. The upper hemisphere is enveloped in a 
cloth to prevent the condensation of the vapours. 

Drying Agents for Liquids. — Liquids are dried (deprived of 
water) either by placing in them, or in a solution of them, drying 
agents. The most frequently employed drying agents are : 



METHODS OF DRYING 49 

Calcium chloride, 

(a) granulated, 

(b) fused, 
Potassium hydroxide, 
Sodium hydroxide, 
Ignited potash, 
Fused sodium sulphate. 

Less frequently used are : lime, barium oxide, anhydrous sodium 
carbonate, anhydrous copper sulphate, phosphorus pentoxide, 
sodium, and others. 

In the choice of a drying agent care must be taken to select 
one which will not react with the substance to be dried. For 
example, calcium chloride unites to form double compounds with 
alcohols as well as with bases. Consequently, for drying these 
two classes of compounds, calcium chloride is never used. Caustic 
potash and caustic soda, as is well known, react with acids and 
phenols to form salts, upon alcohols to form alcoholates, and upon 
esters, saponifying them. These drying agents are never used 
with these substances. Further, acids are never dried with car- 
bonates, owing to the salt formation taking place. 

Calcium chloride is employed in two forms, — granulated and 
fused. The former acts more energetically, since it contains less 
water of crystallisation and possesses a larger acting surface. Still, 
it has the disadvantage of being more porous than the fused 
variety and in consequence of this porosity the loss of the sub- 
stance being dried is greater. For drying small quantities of a 
substance, or liquids containing very little moisture, it is better, 
therefore, to use fused calcium chloride. 

On drying bases with caustic potash or caustic soda, it must be 
borne in mind that these drying agents may be contaminated, 
at times, with potassium nitrite or sodium nitrite. Since these 
latter act upon bases, decomposing them, it is necessary to use 
the pure alkalies, or in place of them potassium carbonate or 
Glauber's salt. 

Methods of Drying. — As already mentioned, liquids may be 



50 GENERAL PART 

dried either in the undiluted form or in solution. The first method 
is followed when the quantity of the liquid is considerable, so that 
the loss of the substance necessarily incident to the adhesion of 
the liquid to the drying agent cannot amount to a large percent- 
age of the whole. Low boiling liquids are always dried directly, 
without the use of a solvent. If a solution of a higher boiling 
compound is to be dried, it is done before the solvent is distilled 
off. A small quantity of a substance or a viscous substance .is 
designedly treated with a diluting agent, generally ether, and 
is then dried. 

The drying is accomplished by placing the drying agent in the 
liquid and allowing the two substances to remain in contact for 
a longer or shorter time, according to circumstances. So long 
as a liquid appears turbid, it has not been deprived of its moisture. 
A liquid about to be dried must never contain drops of water 
which are visible ; in case it does, it must be treated in a separating 
funnel or the water drawn off with a capillary pipette: it is then 
dried. If only a few small drops of water are present, the liquid 
is first filtered through a small folded filter, or it is poured care- 
fully into another vessel, and the water drops will remain in the 
first vessel, adhering to the walls. When a separation of an ethereal 
from an aqueous solution is to be made, to prevent a portion of 
the water from being carried along with the ethereal solution, the 
former is not drawn off through the cock of the vessel, but is 
poured out of the mouth, as has already been mentioned. 

If a liquid contains very much moisture, and this is the case 
especially in turbid, milky liquids, it frequently happens that the 
drying agent will absorb enough water to dissolve itself and thus 
form an aqueous solution. In this case a fresh quantity of the 
drying agent is not added at once, but the separation of the two 
layers is effected by a separating funnel, pipette, or by decanting 
one of the layers. 

A similar rule obtains for undiluted liquids. The drying of 
high boiling substances, if they are not volatile at the temperature 
of the water-bath, may be greatly facilitated by heating them with 
the drying agent on the water-bath. 



FILTRATION 



51 



Before distilling a liquid which has been dried, or before dis- 
tilling off the solvent from such a liquid, it is poured off from the 
drying agent. To obtain the small portions which adhere to the 
latter it may be washed with a small quantity of the dried solvent. 
Low boiling individual liquids (boiling on water-bath) can, under 
certain conditions, be distilled without a previous separation from 
the drying agent. If the liquid to be dried is of such a specific 
gravity that the drying agent will float in it, then, in order to effect 
the separation, it is poured through a funnel containing a small 
quantity of glass wool, or asbestos. In some cases, which, how- 
ever, are rare, a liquid not easily volatile may be dried by expos- 
ing it in a dish as ^hallow as possible in a partially exhausted 
desiccator. 

FILTRATION 

While in analytical operations it is much more desirable to 
conduct filtrations without employing pressure, the precipitates 
obtained in organic preparation work are filtered with pressure 
whenever it is possible. The method presents a number of ad- 
vantages : the filtration may be made in a much shorter time ; the 
liquid may be much more completely sepa- 
rated from the precipitate, in consequence of 
which the latter will dry more rapidly, etc. 

The student has already learned the meth- 
ods of filtering without pressure in the opera- 
tions of analytical chemistry, but he is advised 
to reread the chapter on Crystallisation (see 
page 1). 

Filtration with Suction. — For filtering un- 
der pressure (suction), a filtering flask a (suc- 
tion flask) with a side-tube b (Fig. 35) is used. 
An ordinary flask may be converted into a 
suction flask by fitting to it a two-hole rubber 
stopper ; through one hole is passed the stem 
of a funnel, through the other a glass tube, 
bent at a right angle, one end of which passes just through the cork, 




52 GENERAL PART 

while the other is attached to the suction. For this purpose flasks 
with thick walls are selected, in order that they may not be crushed 
by the atmospheric pressure on exhaustion; if a thin-walled flask 
is used, it must be exhausted but slightly. 

The funnel used is, in many cases, the ordinary conical glass form, 
in which is placed the filter. If the funnel is imperfect in construc- 
tion, and does not possess the correct angle (6o°), the filter is made 
narrower or wider, as the case may be, to accommodate it to the 
angle of the funnel. In order that the point of the filter not sup- 
ported by the glass walls of the funnel, may not tear on exhaustion, 
a platinum cone c is previously placed in the funnel. 

If a platinum cone is not at hand, it may be replaced by a coni- 
cally folded piece of parchment paper or filter-cloth. The filter 
is moistened with the same liquid which is to be filtered, otherwise 
it may happen that the filtration is prevented, or, at least, rendered 
difficult ; e.g. if the v filter has been moistened with water, and an 
alcoholic solution is to be filtered through it, the substance dis- 
solved in the alcohol may be precipitated in the pores of the filter 
by the water. If a liquid foams excessively on filtering, as happens 
at times with alkaline liquids, the rubber tubing is removed sud- 
denly from time to time from the filter-flask. The pressure of the 
in-rushing air destroys the bubbles. The foaming may also be pre- 
vented at times by treating the filtrate with a few drops of alcohol 
or ether. This is one of the common methods of preventing foam- 
ing in general. When filtering very small quantities of a liquid, a 
test-tube is placed in the filter-flask, as is represented in Fig. 36. 

The suction surface may be increased by placing a so-called 
filter-plate of glass or porcelain in the funnel (Fig. 37). If a 
filter-plate is used, the filter-paper should be of two thicknesses. 
Upon the plate is first placed a round filter of exactly the same 
size as the plate, and upon this another round filter, the edge of 
which projects about 2-3 mm. beyond that of the plate. 

The Btichner funnel is indispensable in working with organic 
substances. In consequence of its large suction surface, a very 
rapid filtration is possible. In the filtration of large quantities 
of substance it should always be used (Fig. 38). 



FILTRATION 



53 



A double filter (described above) may be used in this, but in 
most cases a single filter is sufficient. Since the Btichner funnels 
are made of porcelain, and consequently are opaque, they must be 
carefully cleaned immediately after using. 






Fig. 36. 



Fig. 37. 



Fig. 38. 



Similar to the Biichner funnel in its construction and action is 
the so-called "Nutsch " filter. This consists of a shallow dish with 
a perforated bottom, which is 
fitted to the cover of a tubu- 
lated cylinder by means of a 
rubber ring, the joint being 
air-tight. This apparatus is 
especially adapted to the filtra- 
tion of larger quantities than 
can be conveniently treated in 
the Biichner funnel (Fig. 39). 

If the solution to be filtered 
acts on the filter-paper, filter- 
cloth may be used in its place. 
A fine or coarse meshed cloth 
is selected, according to the 
nature of the precipitate; it is 
moistened before the nitration 

If this is also attacked, nitrocellulose cloth may be used ; it is 
made by treating a cloth woven from plant fibres with a mixture of 




54 



GENERAL PART 



nitric and sulphuric acids. Concentrated sulphuric acid may be 
filtered through it. Such cloth and other substances containing 
nitrocellulose must always be preserved under water, on account 
of their explosiveness. 

In cases of this kind the precipitate is retained by using glass 
wool, or better, long fibrous asbestos, with which the bottom of the 
funnel, containing in this case a platinum cone, is filled, or it is 
spread out in thin layers over a filtering plate, or on the surface of 
a Buchner funnel. Under these conditions, the suction is applied 
gently at the beginning of the filtration ; as soon as a large quantity 
of the precipitate has accumulated, the suction is increased. Very 
coarse-grained precipitates can be filtered without the use of a filter 
by placing in the point of an ordinary glass funnel a sphere of glass (a 
marble) ; this is surrounded by glass wool, or asbestos, if necessary. 
Pukall Cells. — For the filtration of precipitates, like calcium 
sulphate, barium sulphate, of strongly acid liquids, etc., Pukall's 

cells (porous cells), made of 
unglazed clay, are very use- 
ful. They may be procured 
in different sizes in the mar- 
ket, and possess either the 
form of a cylinder or a mor- 
tar pestle. The operation is 
performed as follows : In the 
mouth of the cell is placed a 
closely fitting stopper bearing 
a glass tube bent twice at right angles, connected with a filter- flask. 
The tube at each end projects slightly below the stopper (Fig. 40). 
The cell is now immersed in the liquid to be filtered, contained in 
a beaker, not too wide, until it almost touches the bottom. When 
the suction is applied, the liquid filters through the porous walls 
until the cell is filled, and is then drawn into the flask ; the pre- 
cipitate remains behind in the vessel, and for the most part is 
deposited on the exterior walls of the cell. 

Filter-Press. — For the filtration of large quantities of substances 
which filter with difficulty, especially dye-stuffs, barium sulphate, 




Fig. 40. 



SEPARATION OF LIQUID MIXTURES 



55 



calcium sulphate, etc., fil- 
ter-presses are often used, 
of which the Hempel form 
will be described (Fig. 41). 
The separation of the liquid 
from the precipitate is ef- 
fected in the cell c, which 
consists of two perforated 
porcelain plates between 
which is a rubber ring. The 
first operation in working 
with the press is the prepara- 
tion of the cells. Two circu- 
lar pieces of filter-cloth and 
two of filter-paper the same 
size as the plates are cut; 
after the cloth (linen or 
muslin) has been thoroughly 
moistened with water, the 
cells are made as follows : 
At the bottom comes the 
perforated plate upon which 
is placed one layer of the 
filter-paper, and upon this 
the cloth. After a wide glass 
tube g, which extends almost 
to the opposite side of the 
cell, has been inserted into 
the opening of the rubber 
ring, this is placed upon the 
cloth, then follows the other 
piece of cloth, filter-paper, 
and finally the second plate. 
The cell is now secured by 
three clamps, one of which 
is attached near the glass 




Fig. 41. 



56 



GENERAL PART 



tube, and the others equally distant from this. The cell is now 
ready for the filtration, and is placed between the two corrugated 
glass plates d. Before it is connected with the vertical tube b, the 
pinch-cock on this is closed, water is poured into the funnel a, 
and the cock is now opened until the vertical tube is filled. The 
cock is again closed and the tube is connected with the cells, the 
liquid to be filtered poured into the funnel and the cock opened. 
During the resulting filtration care is taken to keep the funnel 
partially filled so that the vertical tube is constantly full. If the 
first portions run through turbid, they are returned to the funnel. 
In order to wash the precipitate collecting in the cell, the glass 
tube passing through the rubber ring is partly withdrawn, so that 
it projects into the cell but a few centimetres. This causes a 
canal to be formed in the cell from which the wash water can 
permeate the precipitate in all directions. If the precipitate is 
large enough to completely fill the interior space of the cell, it 
forms a solid cake that can be removed without difficulty. But 
if the precipitate is small, and it is desired to obtain it, the glass 
tube is withdrawn from the rubber ring, the contents of the cell, 

generally half-fluid, are 
poured into a beaker, 
the cell taken apart, and 
the precipitate adhering 
to the sides scraped off 
with a spatula. By fil- 
tering with suction a 
complete separation of 
the liquid and precipi- 
tate is effected. If it is 
desired, to filter larger quantities of a precipitate than can con- 
veniently be done in a single cell, two cells connected by a Y-tube 
may be used. 

Filtering through Muslin. — Precipitates which are not too 
finely divided may be filtered off through a filter-cloth (muslin) 
stretched over a wooden frame (filter-frame) (Fig. 42). A square 
piece of muslin or linen, after being thoroughly moistened, is 




Fig. 42. 



FILTRATION 57 

fastened on the four nails of the frame is such a way as to cause 
a shallow bag in the middle. The frame is placed over a dish of 
the proper size and the liquid to be filtered is poured on the 
cloth and generally filters rapidly through it. If it is desired after 
washing the precipitate to press it out, the cloth is taken from 
the four corners, folded together, and squeezed with the hands. 
The precipitate may be further dried, by tying up the opening 
of the bag with twine, and then pressing it out carefully under a 
screw-press. 



58 GENERAL PART 



HEATING UNDER PRESSURE 

Sealed Tubes. Method of Filling. — If it is desired to induce 
a reaction between two substances at a temperature above their 
boiling-points, .they are generally heated in sealed tubes. If a 
quantitative determination is not to be made, if the substances 
to be heated do not attack the glass or generate no gases, and if 
the heating is not to be high, soft glass tubes may be used. But 
generally, and in quantitative determinations always, difficultly 
fusible tubes of potash glass are used, since they are not so easily 
acted upon and do not crack so readily as the former. In filling 
the tubes the following points are observed. The tube is dried 
before placing the substance in it. Never put solid or liquid 
substances directly in the tube, but with the aid of a funnel-tube 
which should be as wide as possible when the substance is a solid. 
In proportion to the temperature of the heating a greater or less 
pressure is developed ; therefore more or less of the substance is 
placed in the tube, depending on the conditions. The tube is 
never more than half-filled. Easily volatile substances as well 
as those giving off vapours, like hydrochloric and hydriodic acids, 
which render the sealing of the tube difficult, are transferred to 
the tube just before the sealing is to be done. In withdrawing 
the funnel-tube care is taken to avoid bringing it in contact 
with the walls of the tube. 

Sealing. — To seal the open end of a tube charged with the 
substance, it is warmed by holding it at an angle of about 45 , 
with constant turning, in the small luminous flame of a blast- lamp, 
and then heated strongly in a larger non-luminous flame ; when 
the glass becomes soft, a previously somewhat warmed glass rod 
is fused to it (Fig. 43, I). The flame is then applied to the tube 
at a short distance from the opening, and as soon as the glass has 
become soft the tube is narrowed by drawing it out suddenly (II). 
After breaking off or cutting off the end of the capillary tube at 
<z, to allow the air to escape on further heating, it is heated at b, 
when the tube is softened at this point it is drawn out slightly, 



HEATING UNDER PRESSURE 



59 



the heat is applied just below b, it is drawn out again, and so 
on ; the result is that the form of the end of the tube gradually 
changes from a cylinder to a sharp-pointed cone. The narrowest 
part of the latter is then heated with a not too large flame 
without drawing it further. The soft glass melts together, and 
there is thus obtained a thick-walled capillary tube which is 
melted off at the proper place (III). Figure 44 shows the 
sealed portion of a tube in its natural size. In the formation of 





Fig. 44. 



the capillary portion, it is desirable not to turn the tube in the 
manner previously directed, but to give it a few turns in one direc- 
tion and then to reverse the motion, otherwise a spiral would be 
formed owing to the smallness of the glass at that point. After 
sealing, the heated portion is cooled gradually by holding it in 
the luminous flame until it is blackened. The sealing of hard 
glass tubes may be facilitated by placing a brick or tile near the 
flame in such a position that the heat will be reflected. If one 



60 GENERAL PART 

is in possession of a cylinder of oxygen, it may be attached to 
the blast-lamp in place of the blast. At the high temperature 
of the illuminating gas-oxygen name, the sealing may be effected 
with great ease. 

In many cases the operation is rendered difficult by the vapours 
of the substance attacking the glass, or by the decomposition of 
the substance with the evolution of troublesome products like 
carbon, iodine, etc. Under these conditions, the tube is not 
drawn out first to a narrow tube, as above, but the glass rod 
fused on is allowed to remain, and this is used to draw out the 
tube. The sealing is rendered less difficult by allowing the air 
to have free access to the tube, in order that the evolved vapours 
may pass out unimpeded. The separation of carbon may be 
avoided by having an assistant direct a continuous current of air, 
during the heating, through a narrow tube into the upper part 
of the tube being sealed ; this will cause the oxidation of the 
carbon. When dealing with very volatile substances, during the 
sealing the lower part of the tube is cooled by water, ice, or a 
freezing mixture. In this case, the services of an assistant will 
be needed to give to the vessel containing the cooling agent a 
circular motion corresponding to that of the tube. Under these 
conditions, it is often advisable to narrow the tube before charging 
it with the substance, so that it will just admit a funnel-tube as 
narrow as possible. 

Heating. — The heating of sealed tubes (bombs) is conducted 
in the so-called " bomb-furnace," of which a convenient form is 
represented in Fig. 45. To be able to carry out the operation of 
heating at a definite temperature, a cork, covered with asbestos 
paper, bearing a thermometer, is fitted into the opening at the 
top of the furnace. The bulb of the thermometer must be about 
1 cm. above the bottom of the iron tube. The sealed tube is not 
heated directly, but in a thick-walled protecting case of iron 
closed at one end, in which the glass tube is so placed that the 
capillary portion is at the open end. In transferring the glass 
tube to the iron casing the latter is not held vertically, but is 
slightly inclined from the horizontal, so that the glass tube may 



HEATING UNDER PRESSURE 



61 



not be broken by suddenly striking the bottom. The iron case 
is pushed into the furnace open end first, so that in case cf an 
explosion the fragments of glass are not thrown out of the for- 
ward end but from the rear of the furnace, directed toward a wall. 
A " fragment cage " renders the flying pieces of glass harmless. 
After the tube is in position the front opening is closed by a 
" drop-slide." The tubes are not heated at once up to the desired 
temperature, but are warmed gradually. If it is desired to 
heat a furnace similar to the one represented to a low tempera- 
ture, the gas tubes are raised and small flames used, rather than 
a lowering of the gas-tube and the corresponding increase in size 




Fig. 45- 



of flame. The danger of the bursting of the glass tubes may 
be diminished in many cases, particularly in those in which a 
very high pressure is developed, by interrupting the heating after 
a certain length of time, opening the capillary after the tube has 
completely cooled, and allowing the gases which have been gen- 
erated to escape. The tube is then resealed and heated again. 

If tubes are to be heated not higher than ioo°, the convenient 
so-called " water-bath cannon" is used, in which the case enclos- 
ing the tube is heated by steam at ordinary pressure ; in this case 
overheating is impossible. 

Opening the Tubes. — Sealed tubes must not be opened until 
after they are completely cold. The protecting case of iron, con- 
taining the tube, is removed from the furnace and held in a slightly 



62 GENERAL PART 

inclined position, the end of the capillary being higher than the 
rear end. By means of a slight jerk the capillary end of the glass 
tube is caused to project from the iron case. The extreme end 
of the capillary is now held in the flame of a Bunsen burner. In 
case there is an internal pressure in the tube, the glass on becom- 
ing soft will be blown out and the gases will escape from the 
opening thus made, often with such force as to extinguish the 
flame. If on the softening of the glass the capillary is not blown 
out, it may be due to the absence of internal pressure or the tube 
may be stopped up by some of the substance. In the latter case 
the substance is removed by heating. To show that there is an 
internal pressure the capillary is held after it has been opened 
near a small luminous flame ; if the latter is blown out in a long 
thin flame sidewise, obviously there is pressure. If great pressure 
exists in a tube to be opened, before blowing the capillary the 
hand holding the iron casing is protected by a thick glove or a 
cloth is wrapped around the casing several times at the point 
where it is held, so that if the tube bursts, in consequence of the 
sudden diminution of pressure, and the seam of the case should 
be torn open, the hand is protected from injury. In handling an 
unopened' tube the greatest care possible must be observed. It is 
never removed from the iron casing to look at it or for any other 
purpose. On opening, it is held in such a position that neither 
the operator nor any one else can be injured in case of bursting. 

On heating substances with hydriodic acid and phosphorus, it 
sometimes happens, that the tube on being opened by a flame, 
explodes. In this case the explosion is due to the fact that the 
phosphine as well as the hydrogen evolved in the reaction have 
formed an explosive mixture with the oxygen of the air present 
in the tube. Under these conditions, the capillary is opened by 
snipping off the end with pincers or tongs, but in doing so the 
greatest care must be observed. To remove the end of the cone, 
it is not necessary to proceed as described below, but the end 
of the tube is broken directly with a blow of a hammer. 

In order to break off the end of a tube after it has been opened } 
so that the contents may be emptied out, the procedure is as 



HEATING UNDER PRESSURE 6$ 

follows : At that point of the tube where the cone begins, a well- 
defined file mark is made, not extending completely around the 
tube ; this is touched lightly with the hot end of a glass rod, 
previously heated to fusion in the blast-flame. If the crack caused 
by this does not extend entirely around the tube, the extreme 
end of it is again touched with a hot glass rod, by which it is 
extended, so that the conical end may be lifted off. Instead of a 
glass rod, a thick iron wire, the end of which has been bent around 
the iron casing to a semicircle, may be used. If this is heated 
to redness, the file mark touched with it, and the wire turned, the 
end of the tube breaks off smoothly. To prevent the fragments 
of glass from falling into the tube (when a quantitative determina- 
tion is being made), the method of procedure is this : As before, 
a deep file mark is made,, and on each side of it, at a distance 
of ^ cm., a strip of moistened filter-paper i cm. wide is wrapped 
around the tube several times. That portion of the tube between 
the strips is heated by a small flame, the tube being con- 
stantly turned, this causes the end to split off smoothly 
without splintering. If the glass does not crack at once, 
the heated portion is moistened with a few drops of / 
water, and the breaking off will follow with certainty. 

Volhard Tubes. — The tube described by Volhard 
(Fig. 46) may be used to great advantage when it is 
desired to heat large quantities of substances in a single 
tube. It consists of a wide tube to the end of which a 
narrower one is fused. A tube of this kind, 35 mm. in 
diameter and 45 cm. in length, contains about \ of a 
litre, and possesses the further advantage of being easy 
to seal. If on opening the tube care be taken, to cut 
off as small a portion of the narrow end as possible, 
it may be used repeatedly. If, finally, the narrowed 
portion becomes too short, another piece of the same 
kind of tubing is sealed on. - ig. 4 . 

Pressure Flasks. Autoclaves. — In order to heat substances 
under pressure at a moderate temperature which on reacting with 
each other evolve no gaseous products, so that no pressure due 



64 



GENERAL PART 




to the reaction is developed, they are sometimes enclosed in 

strong- walled flasks (pressure flasks), wrapped up in a cloth and 
heated in a water-bath. 

Very well adapted to this purpose are the common 
soda-water or beer bottles, of the kind represented 
in Fig. 47. In using them they are not immersed in 
water already heated, but are slowly heated with the 
water. The water-bath is closed by a loosely fitting 
cover, so that in case the bottle bursts, one may not 
be burned by the hot water. The flasks are not 
opened until after they are 
completely cold. 
1G ' 47 ' Large quantities of sub- 

stances which do not act on metals may 

be heated under pressure in closed ves- 
sels, generally made of iron, bronze or 

copper (autoclaves). Such vessels are 

not suited for heating acid substances, 

but may be used for neutral or alkaline 

substances. In this laboratory Mannes- 

mann tubes (without seams) are in use, 

one end being welded together, and the v 

other is supplied with a screw-thread 1 

and cap. The open end is cone-shaped, eaj' 

The tube is closed by a threaded cap, 

which in section shows a cone. The cap 

is partially filled with lead. After the 

substance has been put in, the cover is 

screwed on as far as possible with the 

hand, the tube is then clamped in a 

vise, and j the cap made fast with a 

wrench. The conical end of the tube is 

pressed into the soft lead, thus giving 

an excellent joint. The heating may be 

conducted in an oil-bath, or directly in the bomb-furnace. If the 

heating is to be carried beyond the point at which lead softens, a 




HEATING UNDER PRESSURE 6$ 

short metallic condenser about 10 cm. in length may be screwed 
on the threaded portion of the tube. A slow current of water is 
passed through the condenser. Tubes of this kind have proved 
of excellent service in many cases, e.g. for the preparation of the 
phenol ethers. 

Another form of autoclave is represented in Fig. 48. For the 
packing a ring of lead or asbestos is used. The tube leading to 
the interior is designed for a thermometer. The lower portion 
contains oil in which thethermometer is placed. 



66 



GENERAL PART 



MELTING-POINT 



In organic work the most common method of testing the 
purity, of characterising and of recognising a solid compound, 
is the determination of its melting-point. The apparatus most 
generally used for this purpose is represented in Figs. 49 and 50. 
A long-necked flask is closed by a cork provided with several 
canals cut in the sides, through which the heated air and vapours 

may escape, bearing a thermometer. 
The bulb of the flask is two-thirds 
filled with pure concentrated sul- 
phuric acid, into which is dropped 
a crystal of potassium nitrate the 
size of a pin-head, to prevent it 
from becoming dark in colour. The 
substance is placed in a small nar- 
row tube (melting-point tube), made 
in the following way : A glass tube 
4-5 mm. wide is heated at one point 
while constantly turned, in a small, 
blast-lamp flame, until it becomes 
soft, and is then drawn out from 
— Q, both ends to a tube 1 mm. wide. 
The narrow tube thus produced is 
then fused off at its middle point ; 
the portion lying next to that part 
of the glass tube which has not been drawn out is heated as 
before and is again drawn out, and so on. There is thus pro- 
duced a tube having the form represented in Fig. 51 a. In 
order to prepare the melting-point tube from this a file-mark is 
made at the points indicated, the tube broken off and fused at 
the narrow end by holding it nearly vertical in a Bunsen flame. 
Fig. 51 b represents the melting-point tube in its natural size. 
A supply of several dozen of these is made and preserved in a 
closed bottle. To transfer to the tube the substance the melt- 




FiG. 49. 



Fig. 50. 



MELTING-POINT 



6 7 



a 



ing-point of which is to be determined, a small portion of it is 
pulverised, the end of the tube dipped into it ; by gentle tapping 
the substance is caused to fall from the upper end to the bot- 
tom of the tube. In order that it may not form a 
too loose layer, it is packed by a thin glass rod or 
platinum wire. The height of the layer should be 
1 mm. and in no case more than 2 mm. To attach 
the tube different methods may be used. The 
upper end of the tube may be touched with a drop 
of sulphuric acid; this, when brought in contact 
with the thermometer, will cause it to adhere. It 
is safer to fasten the tube, just below the mouth, to 
the thermometer with a thin platinum wire or a 
rubber ring 1 mm. wide. The substance is placed 
at the middle point of the thermometer bulb. 
The thermometer is now immersed in the sul- 
phuric acid until the bulb is at about the centre of 
the liquid ; the flask is heated with a free flame 
which is given a continuous, uniform motion as in 
distillation. The burner is inclined at a conven- 
ient angle, so that, if the flask should break, the 
hand would not be directly under it. When the 
melting temperature is reached, it is observed that 
the previously opaque, unfused substance suddenly 
becomes transparent and a meniscus is formed on 
its upper surface. If it is known at about what 
point the substance will melt, it may be heated 
rapidly to within io° of this point, and then slowly 
with a small flame so that the behaviour of the sub- 
stance from degree to degree can be easily observed. 
If the melting-point is not known, it can be readily 
ascertained on heating it rapidly to a high tempera- 
ture. In this case the determination is repeated, heating rapidly 
until the temperature approaches the melting-point, and then 
slowly. In many cases when the temperature nears the melting- 
point this is shown by a softening of the substance before melt- 



a b 

Fig. 51. 



68 



GENERAL PART 



ing; it loosens from the walls of the tube and collects in the 
middle. If this phenomenon occurs the heating is conducted 
very slowly from degree to degree. At times proximity to the 
melting-point may also be recognised by the fact that the par- 
ticles of the substance which adhered to the upper portion of 
the tube during the filling, melt before the mass of the sub- 
stance ; since the hotter and therefore lighter layers of the acid 
rise to the top, the upper layers of the 
* bath are heated somewhat higher than 

*«k^ I tne l° wer - 

^^MnBWiM Instead of the apparatus just de- 

jp scribed the one represented in Fig. 52 

serves very well for the same purpose. 
The liquid used may be water or sul- 
phuric acid, depending on the melting- 
point of the substance to be examined, 
or in case of a substance with a high 
melting-point paraffin is placed in a 
beaker supported on a wire gauze. In 
order to keep the liquid at a uniform 
temperature, it is stirred by an up-and- 
down motion of the glass stirrer a. 

A substance is regarded as pure in 
most cases, if it melts sharply within 
one-half or a whole degree, and if after 
repeated crystallisation the melting-point 
does not change. In determining the 
melting-point of a newly discovered sub- 
stance, one determination is not sufficient even if it is very sharp ; 
a small portion is recrystallised and the melting-point again deter- 
mined. Many substances decompose on fusing, if this takes place 
suddenly at a definite temperature, this may also be regarded as 
a characteristic of the substance. 

Since many compounds on heating decompose explosively, and 
since in the last few years it has happened that the explosion of 
minute quantities of a compound has shattered the melting-point 




Fig. 52. 



MELTING-POINT 69 

apparatus, and serious wounds have been caused by the hot 
sulphuric acid, it is safer before the melting-point of a hitherto 
unknown substance is determined in the apparatus described 
above, to take the slight trouble of making a preliminary test by 
heating a small tube containing the substance directly in a small 
flame to the melting temperature, and by this means ascertaining 
if the substance will explode. 

Testing the Thermometer. — At this point a few observations 
concerning the testing and correcting of the thermometer will be 
added. Since the ordinary thermometers, at least the cheaper 
varieties, are never exact, they must be corrected before using. 
If a normal thermometer is at hand, the correction to be applied 
may be determined by slowly heating the thermometer to be tested 
by the side of the normal instrument in a bath of sulphuric acid, 
glycerol, or vaseline, and noticing the reading of both thermometers 
for every io°. There is thus obtained a table from which the cor- 
rections may be read directly. For many purposes it is sufficient 
to determine the deviation at only a few points ; the corrections 
for the degrees lying between these may be calculated by inter- 
polation. Thus, e.g., the point to be considered as the true zero 
point may be determined as follows : A thick-walled test-tube of 
about 2\ cm. in diameter and 12 cm. in length is one-third filled 
with distilled water. The mouth is closed by a cork bearing a 
thermometer dipping into the water. Through an opening cut 
out of the side of the cork is introduced a thick copper wire, the 
end of which is bent into a circle at a right angle to its length. 
The test-tube is surrounded by a freezing mixture of ice and salt. 
The water is frequently agitated with the stirrer ; the temperature 
at which crystals first begin to form is carefully noted. 

The true ioo° point is found by placing distilled water in a not 
too small fractionating flask and determining the boiling-point of it, 
the entire column of mercury being in the vapour. In an analo- 
gous manner, the boiling-point of naphthalene (218 at 760 mm. 
pressure) and of benzophenone (306 at 760 mm. pressure) may 
serve for the correction of the higher degrees. Since the boiling- 
point is influenced by the pressure, the barometer must be read at 



70 



GENERAL PART 



the same time with the thermometer and a correction, taken from 
the table given below, applied. 



Pressure. 


Water. 


Naphthalene. 


Benzophenone. 


720 mm. 


98.50 


215-7° 


303-5 


725 


98.7 


2l6.0 


303.8 


730 


98.9 


216.3 


304.2 


735 


99.I 


2l6.6 


304-5 


740 


99-3 


216.9 


304.8 


745 


994 


217.2 


305.2 


750 


99.6 


217.5 


305.5 


755 


99.8 


217.8 


305.8 


760 


100. 


218. 1 


306.I 


765 


100.2 


2l8.4 


306.4 


770 


100.4 


218.7 


306.7 



DRYING AND CLEANING OF VESSELS 



While in analytical operations, since one generally deals with 
aqueous solutions, the cleaned vessels may be used even if wet, it 
frequently happens in organic work, in experimenting with liquids 
not miscible with water, that dry vessels must be employed. In 
order to dry small pieces of apparatus rapidly, they should be 
rinsed first with alcohol and then with ether. To remove the last 
portions of the easily volatile ether, air from a blast is blown 
through the vessel for a short time, or the ether vapours are 
removed by suction. The alcohol and ether used for rinsing can 
frequently be used again ; it is convenient to keep two separate 
bottles for the wash alcohol and wash ether, into which the sub- 
stances, after being used, may be poured. 

For rapid drying of large vessels this method is costly. In this 
case the procedure is as follows : The wet vessel is first drained 
as thoroughly as possible, and then heated with constant turning 
in a large luminous blast-flame, while, by means of a blast of air 
from bellows or other source, the water vapour is driven out. It 



DRYING AND CLEANING OF VESSELS 7 1 

may also be removed by careful heating and simultaneous suction. 
Thick-walled vessels like suction flasks must not be heated over 
a flame, but are dried by the first method. 

Vessels may be cleaned in part by rinsing them out with water 
with the use of a feather or flask-cleaner. If the last portions 
of the solution of a solid, e.g. in alcohol, are to be removed from 
a flask, it is not washed out at once with water, but first with a 
small quantity of the solvent, and then afterwards with water. 
If the vessel contained a liquid not miscible with water, it is first 
washed with alcohol and then with water. Resinous or tarry 
impurities adhering firmly to the walls can be removed by crude 
concentrated sulphuric acid. The action of this latter may be 
strengthened by adding a little water to it, by which heat is gener- 
ated ; also by the addition of some crystals of potassium dichro- 
mate. At times the impurities adhere so firmly that the vessel 
must be allowed to stand in contact with sulphuric acid for a long 
time. Crude concentrated nitric acid, or a mixture of this with 
sulphuric acid, is also used at times for cleaning purposes. Im- 
purities of an acid character can, under certain conditions, be 
removed by caustic soda or caustic potash. 

Finally, a method for cleaning the hands may be mentioned if 
they are discoloured by dyes which cannot be removed by water. 
If the dye, e.g. fuchsine, contains an amido (NH 2 ) group, the hands 
are dipped into a dilute, weakly acid solution of sodium nitrite. 
The dye is diazotised, and may be removed by washing in water. 
The two methods following are applicable to all dyes ; the hands 
are immersed into a dilute solution of potassium permanganate 
to which some sulphuric acid has been added, and are allowed to 
remain for some time ; the dye is oxidised, and thereby destroyed. 
After the permanganate has been washed off with water, the hands, 
especially the nails, are coloured brown by manganese dioxide. 
This is removed by washing the hands with a little sulphurous acid. 
The second method is this : A thick paste of bleaching powder 
and a sodium carbonate solution is rubbed on the hands. This 
causes the oxidation and destruction of the dye as above. In 
order to take away the unpleasant odour of the bleaching powder, 
the hands are scrubbed with a brush, care being taken to remove 
the particles adhering to the upper and under surface of the nails, 
and are then washed, as just described, with sulphurous acid. 



72 GENERAL PART 



ORGANIC ANALYTICAL METHODS 

DETECTION OF CARBON, HYDROGEN, NITROGEN, SULPHUR, AND THE 

HALOGENS 

Tests for Carbon and Hydrogen. ■ — If on heating a substance on 
platinum foil, it decomposes with charring, it is an organic sub- 
stance. Carbon and hydrogen may be detected in one operation, 
by mixing a small portion of the dried substance with several times 
its volume of ignited fine cupric oxide, placing the mixture in a 
small test-tube, adding more cupric oxide to the top of the mixt- 
ure, and heating strongly, the tube being closed by a cork bearing 
a delivery tube bent twice at right angles. If the gas evolved 
(carbon dioxide) will cause a clear solution of barium hydroxide 
to become turbid, the original substance contained carbon ; if it 
also contained hydrogen, small drops of water will collect in the 
upper cold part of the tube. 

Test for Nitrogen. — To test an organic substance for nitrogen, 
it is heated in a small test-tube of difficultly fusible glass, about 
5 mm. wide and 6 cm. long, with a piece of bright potassium the 
size of a lentil, which has been pressed between layers of filter- 
paper, in a Bunsen flame until decomposition, generally accom- 
panied by slight detonations and dark colouration, takes place. 
The tube is finally heated to redness ; while still hot it is dipped 
into a small beaker containing io c.c. of water; by this the tube 
is shattered, and any potassium unacted upon becomes ignited. 
The aqueous solution containing potassium cyanide, if nitrogen 
was present in the substance, is filtered from the carbon and glass 
fragments, the filtrate treated with a few drops of caustic potash 
or caustic soda until it shows an alkaline reaction ; to this solution 
is then added a small quantity of ferrous sulphate solution and 
ferric chloride solution ; it is boiled 1-2 minutes, and if potassium 
cyanide was present, potassium ferrocyanide will be formed. After 
cooling, the alkaline liquid is acidified with hydrochloric acid, the 



ORGANIC ANALYTICAL METHODS 73 

precipitated ferric and ferrous hydroxides will be dissolved, and 
being acted upon by the potassium ferrocyanide, will form Berlin 
blue. Accordingly, if nitrogen was present, a blue precipitate is 
obtained, otherwise only a yellow solution will be formed. If the 
substance contains only a small proportion of nitrogen, at times no 
precipitate is obtained at first, but only a bluish-green solution. 
If this is allowed to stand some time, under certain conditions, 
over night, the precipitate will separate out. In testing easily 
volatile substances for nitrogen, a longer tube is used and the por- 
tions of substance condensing in the upper cold part of the tube 
flow back a number of times on the potassium. In place of potas- 
sium, sodium may also be used in most cases, but the former acts 
more certainly. In testing for nitrogen, in a substance containing 
sulphur, a larger quantity of potassium or sodium than that given 
above is used (for 0.02 grm. of substance, about 0.2 grm. potassium, 
in order to prevent the formation of an alkali sulphocyanate). 
Substances which evolve nitrogen at moderate temperatures, e.g. 
diazo-compounds, cannot be tested in the manner described. In 
dealing with a substance of this kind it must be determined whether 
on heating the substance with cupric oxide in a tube filled with car- 
bon dioxide, a gas is given off which is not absorbed by a solution 
of caustic potash. (See quantitative determination of nitrogen.) 

In a limited number of substances containing nitrogen, the pres- 
ence of the latter may be proved by heating the substance with an 
excess of pulverised soda-lime in a test-tube with a Bunsen flame ; 
this causes decomposition with evolution of ammonia, which is 
detected by its odour or by means of a black colour imparted to a 
piece of filter-paper moistened with a solution of mercurous nitrate. 
Nitro-compounds, e.g., do not give this reaction. 

Test for Sulphur. — The qualitative test for sulphur is made in 
the same manner as that for nitrogen. The substance is heated 
in a small tube with sodium. After the mass has cooled it is 
treated with water, and to one-half of the solution is added a 
small quantity (a few drops) of a solution of sodium nitroprus- 
siate, just prepared by shaking a few crystals with water at the 
ordinary temperature. A violet colouration indicates the presence 



j a GENERAL PART 

of sulphur. Since the nitroprussiate reaction is very delicate, no 
conclusion as to the amount of sulphur can be drawn from the 
test, therefore the second half of the solution is treated with a 
lead acetate solution and acidified with acetic acid. In propor- 
tion to the amount of lead sulphide formed, the liquid will assume 
a dark colour, or a more or less heavy precipitate will appear, in 
this way indicating the original quantity of sulphur. 

Easily volatile substances cannot usually be tested by this 
method. They are heated with fuming nitric acid in a bomb- 
tube to about 200 or 300 . After diluting with water the solution 
is tested with barium chloride for sulphuric acid. (See method for 
the quantitative determination of sulphur.) 

Test for the Halogens. — The presence of chlorine, bromine, 
and iodine in organic compounds can only in rare cases be shown 
by precipitation with silver nitrate. This is explained by the fact 
that most organic compounds are non-electrolytes; i.e. that the 
solutions of the same do not contain free halogen ions, as is the 
case in solutions of the inorganic salts of the halogen hydracids. 

In order to detect the halogens, the substance to be tested is 
heated in a not too narrow test-tube with a Bunsen flame with an 
excess of chemically pure lime, the tube while still hot is dipped 
into a little water, chemically pure nitric acid is added to acid 
reaction, the solution is then filtered and treated with silver nitrate. 

In compounds containing no nitrogen, a test for the halogens 
may be made by the same method given for nitrogen — heating 
with sodium. In this case the solution, filtered from the decom- 
position products and fragments of glass, is acidified with nitric 
acid and silver nitrate added. Substances containing nitrogen 
cannot be tested in this way for the halogens, since, as shown 
above, these on fusion with sodium give sodium cyanide, which, 
like the sodium halides, reacts with silver nitrate. 

The presence of halogens may be recognised very quickly and 
conveniently by Beilstein's test. A piece of cupric oxide the size 
of a lentil, or a small rod of the oxide \ cm. long, is wrapped 
around with a thin platinum wire, the other end of which is fused 
to a glass handle, and heated in the Bunsen flame until it becomes 



ORGANIC ANALYTICAL METHODS 



75 



colourless. If after cooling, a minute particle of the substance 
containing a halogen is placed on this and then heated in the 
outer part of the flame, the carbon burns first and a luminous 
flame is noticed. This soon vanishes, and there appears a green or 
bluish-green colour due to the vaporisation of the copper halide. 
From the length of time the colour is visible, conclusions may be 
drawn concerning the presence of a trace or more of the halogen 
in the original substance. 

QUANTITATIVE DETERMINATION OF THE HALOGENS 
CARIUS' METHOD 

The method consists in heating a weighed amount of the sub- 
stance to be analysed in a sealed glass tube with silver nitrate 
and fuming nitric acid, by which it is completely decomposed 
(oxidised), and weighing the quantity of the silver halide thus 
formed. 

Requisites for the analysis : 

i. A tube of difficultly fusible glass sealed at one end, length 
about 50 cm.; outside diameter, 18-20 mm.; thickness of 
walls, about 2 mm. (Sealing-tubes, bomb-tubes.) 

2. A funnel-tube about 40 cm. long, for transferring the silver 

nitrate and nitric acid to the glass tube. 

3. A weighing-tube of hard glass (length, 7 cm. ; outside diameter, 

about 6-8 mm.). 

4. Solid silver nitrate and pure fuming nitric acid. The purity 

of the latter is tested by diluting 2 c.c. of it with 50 c.c. of 

distilled water, and adding a few drops of a silver nitrate 

solution. Neither an opalescence nor a precipitate should 
appear. 

Filling and Sealing the Tube. — After the bomb-tube, weighing- 
tube, and funnel-tube have been cleaned with distilled water, they 
are dried, not with alcohol and ether, but by heating over a flame. 
(See page 70, Drying.) The exact weight of the weighing-tube 
is next determined. Into this, with the help of a spatula, is placed 



y6 GENERAL PART 

0.15 to o. 2 gramme of the substance to be analysed, finely powdered. 
The open end of the tube is wiped off with a cloth, and the exact 
weight of the tube plus the substance is found. With the aid of 
the funnel-tube, about 0.5 gramme of finely powdered silver nitrate 
is transferred to the bomb-tube (a correspondingly larger amount 
up to 1 gramme is used for substances containing a high percent- 
age of halogen) and 2 c.c. of fuming nitric acid. If a number of 
halogen determinations are to be made, it is advisable to measure 
off 2 c.c. of water in a narrow test-tube, mark the volume with a 
file on the outside, and then use this to measure the acid for the 
different determinations. After removing the funnel-tube, care 
being taken not to touch the walls of the bomb-tube with it, the 
weighing-tube is inserted in the bomb held at a slight angle, and 
is allowed to slide down to the bottom, but the substance must 
not come in contact with the acid. The tube is now sealed in 
the manner described on page 58. During the sealing, the sub- 
stance must be prevented from coming in contact with the acid. 
Even after the tube is closed, this is not brought about purposely, 
as by violently shaking the tube. 

If the substance to be analysed is liquid, it is placed in the 

weighing-tube with a capillary pipette, otherwise the procedure is 

^^^ just as described. In dealing with easily volatile sub- 

|j§- stances, the weighing-tube is closed by a glass stopper, 

made by heating a piece of glass rod in the blast-flame 

until it softens, and then pressing it on a metal surface 

until a head is formed (Fig. 53). 

Heating the Tube. — After cooling, the tube is trans- 
ferred to the iron protecting case, and heated in the bomb- 
• 53 f urnacCj i n accordance with the directions on page 60. 
The temperature and time of heating depend upon the greater or 
less ease with which the compound is decomposed. In many 
cases, it is necessary to heat aliphatic compounds 2-4 hours at 
a temperature of 150-250 , while aromatic compounds must be 
heated 8-10 hours, and finally up to 250-300 . It is convenient 
to so plan the analysis that the bombs may be sealed in the 
evening, so that the heating may be begun the first thing the next 



ORGANIC ANALYTICAL METHODS JJ 

day. The sealed tube is kept under the hood in the bomb-room, 
in the iron case, over night, which is clamped with its open end 
directed vertically upwards. The tube is never allowed to remain 
at the working table. If the furnace is not loaded, naturally it 
is most convenient to place the bomb at once in that. Since in 
many cases the oxidation begins even at the ordinary temperature, 
pressure is developed in the tube ; therefore, after it has been 
standing over night, it must not be removed from the iron case 
to be examined. The heating is done gradually; at first, with 
a small flame, the gas-tubes being lowered from the furnace. 
Gradually these are raised, and the flames increased in size. The 
following table will show how the heating of a moderately refractory 
substance should be regulated. 

The heating is begun at 9 o'clock a.m. 

From 9-10 the temperature is raised to about ioo°, 

io-ii „ „ „ 150°, 

n-12 „ „ „ 200 , 

12-3 „ „ „ 25 o°, 

3-6 „ „ „ 3°°°- 

If an especially high pressure is generated by the decomposition 
of a substance, the danger of the bursting of the tube may be 
lessened by turning off the gas before leaving the laboratory at 
noon, and then in the afternoon opening the capillary, sealing and 
heating again to a higher temperature. The same method is 
followed in working with a substance so refractory that several 
days' heating is required ; in this case at the beginning of the 
second day the pressure is reduced by opening the tube. 

If two bombs are heated in the furnace at the same time, an 
entry is made in the note-book to show which tube lies to the 
right and which to the left. If this has been neglected, and the 
identity of the two tubes is in doubt, the neglect may be corrected 
by again weighing the two weighing tubes. 

To Open and Empty the Tube. — The perfectly cooled tube is 
opened according to the directions given on page 61. Especial 
care must be taken before heating the capillary to softening in a 



78 GENERAL PART 

large flame, to drive back into the tube by gentle heating over a 
small flame, any of the liquid which may have collected in the 
capillary. Before the conical end is broken off the tube is exam- 
ined to see whether it still contains crystals or oily drops of the 
undecomposed substance. In case it does, the capillary is again 
sealed and the tube reheated ; but if it does not, the conical end 
is removed according to the directions given on page 61. The 
part broken off is first washed free from any liquid or any of the 
precipitate which may have adhered to it, with distilled water, into 
a beaker ; the portion in the tube is diluted with distilled water, 
upon which there is generally obtained a bluish-green solution, 
coloured by nitrous acid ; this is poured, together with the weigh- 
ing-tube into a beaker by inverting the tube, care being taken that 
the sudden falling of the weighing-tube does not break the bottom 
of the beaker. In pouring out the tube-contents, the attention 
should be directed to the open end of the tube and not to the 
liquid in the rear end, otherwise some of the liquid may easily be 
spilled. After the outer open portion of the tube has been washed 
with distilled water the tube is revolved and the precipitate in the 
interior is washed out ; this is repeated as often as may be neces- 
sary. If a portion of the silver halide adheres firmly to the glass, 
it may be removed by loosening it with a long glass rod over the 
end of which has been drawn a piece of rubber tubing (such as is 
used in the quantitative analysis of inorganic substances) and then 
washing it out with distilled water. The weighing-tube is removed 
from the bottom of the beaker with a glass rod or thick platinum 
wire held against the walls above the liquid, washed thoroughly 
inside and out with distilled water, and then raised with the fingers 
and washed several times again. At times the weighing-tube be- 
comes yellow to deep brown in colour due to the formation of 
silver silicate. This is not detrimental to the results of the analysis. 
To filter off and weigh the Silver Halide. — The beaker is now 
heated on a wire gauze until the silver halide has settled to the 
bottom and the supernatant liquid is clear. Since the excess of 
silver nitrate at times packs together with the silver halide to form 
thick, solid lumps, the precipitate is from time to time crushed 



ORGANIC ANALYTICAL METHODS 79 

with a glass rod, the end of which has been flattened out to a broad 
head. After cooling, the silver halide is collected on a filter, the 
weight of the ash of which is known, and washed with hot water 
until, on testing the filtrate with hydrochloric acid, no turbidity 
follows ; the filter, together with the funnel, is then dried in an 
air-bath at 100-no , the funnel being covered with a piece of 
filter-paper. In order to weigh the dry halide, as large an amount 
as possible is separated from the paper carefully, and transferred 
to a watch-glass placed on a piece of black glazed paper. The 
portions which fall on the paper are swept into the watch-glass 
with a small feather. The filter is rolled up tightly, wrapped with 
a platinum wire, and ignited in the usual way over a weighed por- 
celain crucible ; the heating is done only with the outer part of 
the flame, and not with the inner, reducing part. The folded filter 
may also be incinerated directly in the crucible, which is first 
heated over a small flame, and the temperature increased later ; 
the heating is continued until the filter ash appears uniformly 
light. In order to convert the silver which has been reduced in 
the incineration back to the silver halide, the fused residue is 
moistened, by the aid of a glass rod, with a few drops of nitric 
acid, — if the latter method of incineration has been employed, 
only after complete cooling of the crucible : it is now evaporated 
to dryness on the water-bath. It is then treated with a few drops 
of the corresponding halogen acid, and again evaporated to dry- 
ness on the water-bath. The principal mass of the silver halide 
on the watch-glass is transferred to the crucible with the aid of a 
feather, and heated directly over a small flame until it just begins 
to fuse : the crucible is then placed in a desiccator, and allowed to 
cool. If the analysis is intended to be very exact, the principal 
mass of the silver halide may be moistened before fusion, with a 
few drops of nitric acid, and then evaporated on the water-bath 
with the halogen acid. 

Even after taking the usual precautions, it sometimes happens 
that the silver halide is mixed with fragments of glass, which will, 
of course, cause the percentage of halogen to be too high. If the 
substance under examination is silver chloride, and the presence 



80 GENERAL TART 

of glass is noticed in the beaker or on filtering, an error may be 
avoided, by pouring over the completely washed, moist silver 
chloride on the filter, slightly warmed dilute ammonium hydroxide 
several times, then washing the filter with water, and precipitating 
the pure silver chloride in the filtrate by acidifying with hydro- 
chloric acid. If the compound under examination is silver bromide 
or iodide, and glass fragments have been noticed, the analysis is 
carried out to the end in the usual way. To determine the amount 
of glass present, the* silver halide in the crucible is treated with very 
dilute pure sulphuric acid, and a small piece of chemically pure 
zinc is added. In the course of several hours, the silver halide is 
reduced to spongy, metallic silver. By careful decantation, the 
liquid is separated from the silver, water is added and decanted • 
this is repeated several times. It is then treated with dilute nitric 
acid, and heated on the water-bath until all the silver is dissolved. 
After dilution with water, it is filtered through a quantitative filter, 
the undissolved glass fragments are also well washed on the filter, 
and the latter incinerated. The weight of the glass is to be sub- 
tracted from the weight of the halide obtained. It is obvious that 
the purity of the fused silver chloride may also be tested in this way. 
In conclusion, the atomic weights of the halogens as well as the 
molecular weights of the corresponding silver compounds are here 
given : 

I. (approximate) : 

CI 

CI = 35.5, AgCl = 143.5, lo g^ZQ = °-39338 - 1 

Br = 80.0, AgBr = 188.0, log^-^- = 0.62893 — 1 

I =i27.o,AgI =235.0, log — =0.73273- 1 

II. (exact) : 

CI 

Cl = 35.45, AgCl= 143-38, log ^1 = 0.39313- 1 

Br 
Br = 79.96, AgBr = 187.89, log — ^ = 0.62897 - 1 

I =126.85, Agl = 243-7 8 > lo g ^-| = o-73 2 63- * 



ORGANIC ANALYTICAL METHODS 8 1 

Krister's Modification. — The determination of the halogens 
may be materially facilitated by using 16-20 drops of fuming nitric 
acid instead of 1^-2 c.c. The tube so charged is heated directly 
up to 320-340 , — it is unnecessary to heat it gradually. When 
an ordinary thermometer is employed to register temperatures 
above 300 , the column of mercury frequently parts. A bomb- 
thermometer made by C. Desaga, Heidelberg, Germany, at the 
suggestion of the author, corrects this defect. It contains nitro- 
gen over the mercury column, and possesses but two degree marks, 
corresponding to 320 and 340 . 



QUANTITATIVE DETERMINATION OF SULPHUR 
CARIUS' METHOD 

This method, like the preceding one, depends upon the com- 
plete oxidation of the weighed substance, by heating it with 
fuming nitric acid in a sealed tube. The sulphuric acid thus 
formed is weighed as barium sulphate. The charging, sealing, 
heating, opening, and emptying of the tube are performed in 
exactly the same way as in the halogen determinations ; but in 
this case it is evident that the use of silver nitrate is superfluous. 
Before breaking off the conical end, the tube is examined to see 
that no undecomposed portions of the substance are present ; if 
there should be, the capillary is again sealed and the tube re- 
heated. Before the sulphuric acid is precipitated with barium 
chloride, the bottom of the beaker must be examined for any 
fragments of glass which may be present ; if there are any, they 
are filtered off through a small filter. 

Precipitation of the Barium Sulphate. — The liquid from the 
bomb, diluted with water up to 400 c.c, is heated almost to boiling 
on a wire gauze and acidified with hydrochloric acid ; a solution 
of barium chloride heated to boiling in a test-tube is gradually 
added until a precipitate is no longer formed. This can be easily 
observed by allowing the precipitate to settle somewhat before 
adding more of the solution. The liquid is then heated over a 

G 



82 GENERAL PART 

small flame until the barium sulphate settles at the bottom of the 
beaker and the supernatant liquid is perfectly clear : at times 
from one to two hours' heating may be necessary. After cooling, 
the liquid is filtered, without disturbing the precipitate at the 
bottom, through a small filter the weight of the ash of which is 
known ; the precipitate remaining in the beaker is boiled several 
minutes with ioo c.c. water and filtered through the same filter. 
The precipitate occasionally at first goes through the paper ; in 
case it does, another beaker is placed under the funnel so that the 
entire quantity of liquid need not be refiltered. The precipitate 
is washed with hot water until a portion of the filtrate tested with 
dilute sulphuric acid shows no turbidity. Before throwing away 
the filtrate, barium chloride is added in order to be sure that a 
sufficient quantity was used in the first instance. If a precipitate 
is formed, the above process is repeated and the second precipitate 
collected on the filter containing the first. 

The method just described has the disadvantage that if a 
smaller quantity of water be used for diluting the contents of the 
tube than that given above, the barium sulphate may easily carry 
along with it some barium nitrate, which is only removed with diffi- 
culty on washing with water. Since, in consequence of this, the 
percentage of sulphur is too high, it is for many reasons preferable 
to wash the contents of the bomb into a porcelain dish instead of 
a beaker, and to evaporate the liquid on the water-bath until the 
acid vapours vanish, before adding the barium chloride ; by this 
operation the nitric acid is removed. After evaporating, the res- 
idue is diluted with water, filtered if necessary, from any glass 
fragments, and the operation just described above repeated. 
Under these conditions, too much of an excess of barium chloride 
is to be avoided. 

Ignition and Weighing of the Barium Sulphate. — In order to 
prepare the barium sulphate for weighing, it is not necessary to 
dry it before incineration ; if Bunsen's method is followed, it may 
be incinerated while still moist. With the aid of a small spatula 
or knife the moist filter is removed from the funnel and folded in 
the form of a quadrant. Should any barium sulphate adhere to 



ORGANIC ANALYTICAL METHODS 83 

the funnel, it is removed with a small piece of filter-paper, which 
is incinerated with the main mass. After the filter has been 
carefully folded toward the centre, it is pressed into the bottom 
of a weighed platinum crucible, placed on a platinum triangle in 
such a position that its axis is inclined 20-30 from a vertical 
position. The cover, also inclined at an angle of 20-30 , in the 
opposite direction, however, is supported before the crucible, so 
that the upper half of the opening of the latter is uncovered. 
The burner under the crucible is placed in such a position that 
the flame, which must not be too large at first, is directly under 
the angle formed by the crucible and cover. This will allow the 
ignition of the filter to take place at so low a temperature that 
reduction of the barium sulphate need not be feared. It some- 
times happens that on heating the filter, the gases formed take 
fire at the mouth of the crucible, which, however, does no harm. 
After some time the burner is placed under the bottom of the 
crucible, the flame increased, and the heating continued until the 
residue has become white. The crucible is now placed in an up- 
right position, heated a short time with the full flame, and then 
allowed to cool in a desiccator. It is entirely superfluous to treat 
the barium sulphate with sulphuric acid and then evaporate it ofT. 
If the percentage of sulphur found is too high, this may have 
been caused, under certain conditions, by the fact that in the pre- 
cipitation too great an excess of barium chloride has been used, 
and that the barium sulphate has carried along some of it. This 
source of error may be rectified by treating the ignited barium 
sulphate with water until the crucible is half full, then adding a 
few drops of concentrated hydrochloric acid, and heating on the 
water-bath for fifteen minutes. The liquid is filtered from the pre- 
cipitate through a quantitative filter ; the greatest portion of the 
precipitate remaining in the crucible is again treated with water 
and hydrochloric acid, and the contents of the crucible poured on 
the filter already used ; after washing repeatedly with water, the 
filter and precipitate are again ignited as before. This process 
is obviously only employed when the barium sulphate has 
not been evaporated down with sulphuric acid. For the calcu- 



84 GENERAL PART 

lation of the analysis the atomic and the molecular weights are 
given : 

I. (approximate) : 

S = 32, BaS0 4 =2 33j log g_ =0.13779- 1 

II. (exact) : 

S = 32.o6, BaSQ 4 = 23346, log ^-^- = 0.13775 - 1 

Simultaneous Determination of the Halogens and Sulphur. — 

If a substance contains both a halogen and sulphur, they may be 
determined in a single operation by the following method : As in 
the determination of the halogens the bomb is charged with silver 
nitrate and nitric acid, and the silver halide filtered off after the 
heating as above described. The filtrate thus obtained contains, 
besides the excess of silver nitrate, the sulphuric acid formed 
by oxidation. This latter cannot be precipitated as before with 
barium chloride, since the silver as silver chloride would also be 
thrown down. In its place is used a solution of barium nitrate, 
the purity of which has been tested by adding silver nitrate 
to it. The precipitation is made hot as above directed, the 
solution used being as dilute as possible — the volume of which 
must be at least 500 c.c. A large excess of barium nitrate is 
particularly to be avoided. If the barium nitrate solution con- 
tains halogen salts as impurities, it is heated, and silver nitrate 
added so long as a precipitate is formed, the precipitate filtered 
off, and the solution, which is now free from halogens, is used 
for the precipitation. 



ORGANIC ANALYTICAL METHODS 85 

QUANTITATIVE DETERMINATION OF NITROGEN 
DUMAS' METHOD 

In scientific laboratories, the method almost exclusively used 
for determining nitrogen quantitatively is that of Dumas. The 
principle involved is that the substance is completely burned by 
cupric oxide in a tube filled with carbon dioxide, the nitrogen is 
evolved as such, and its volume measured, while the carbon and 
hydrogen are completely oxidised to carbon dioxide and water. 

Requisites for the analysis : 

1. A combustion tube of difficultly fusible glass, 80-85 cm - l° n S t 

outside diameter, about 15 mm. 

2. A glass funnel- tube with wide stem (at least 10 mm. in 

diameter) . 

3. 400 grammes of coarse and 100 grammes of fine cupric oxide. 

The former is kept in a large flask, the latter in a small 
one, both of which are closed by a cork covered with tin- 
foil. 

4. 500 grammes of magnesite, in pieces the size of a pea. The 

fine powder, which cannot be used, is sifted out in a wire 
sieve. The dark grains which have become discoloured 
by impurities are thrown out. 

5. A small flask of pure methyl alcohol (50 grammes) for reduc- 

ing the copper spiral. 

6. A copper spiral, 10-12 cm. long. This is made by winding 

an oblong piece of copper wire gauze spirally around a 
thin glass rod. It is made of such a width that when in 
position it will touch the walls of the combustion tube ; 
a space between the walls and spiral is disadvantageous. 
Also a short copper spiral from 1-2 cm. long. 

7. A solution of 150 grammes of potassium hydroxide in 150 

grammes of water. It is prepared in a porcelain dish, 
and not in a glass beaker or flask, since these are fre- 
quently broken by the heat generated by the solution. 
After cooling, it is preserved in a well-closed bottle. 



86 GENERAL PART 

8. A nickel crucible 6 cm. high ; diameter of top 7 cm., for the 

ignition of the coarse cupric oxide. 

9. A moderately large porcelain crucible for the ignition of the 

fine cupric oxide. 
10. A small mortar with a glazed bottom. 

Besides these, a weighing-tube, a one-hole rubber stopper for 
closing one end of the combustion tube, a sieve to sift the copper 
oxide, a small feather, thermometer, absorption apparatus, and a 
eudiometer. 

Preparations for the Analysis. — The analysis is conveniently 
begun by heating the entire quantity of coarse copper oxide in 
the nickel crucible over a large flame (Fletcher burner), and 
the fine copper oxide in the porcelain crucible over a Bunsen 
flame for a long time, the crucibles being supported on wire tri- 
angles. The covers are placed on the crucibles loosely, and 
the copper oxide occasionally stirred with a thick wire. While 
the copper is being heated, one end of the combustion tube is 
sealed to a solid head, the narrower end being selected for this 
purpose, if the tube is not perfectly cylindrical. The sealing is 
done as follows : The end of the tube is first warmed in a luminous 
flame, with constant turning ; it is then heated to softening, in the 
blast-flame, a glass rod fused on it, and the heated portion suddenly 
drawn out to a narrow tube. The glass rod is now fused off, and 
the conical part of the tube just produced is heated and drawn 
out. The cone is then heated in the hottest flame until it falls 
together ; it is finally allowed to cool gradually over a small 
luminous flame. When this operation is finished, the open end 
of the tube is warmed in a luminous flame, and, with constant 
turning, the sharp edges are rounded by the blast-flame : it is then 
allowed to cool in the luminous flame again. After complete 
cooling, the soot is removed, the tube rinsed out several times 
with water, the water allowed to drain off as completely as possible, 
and the tube finally dried in one of the two following ways : The 
tube, with constant turning, is repeatedly passed through the large 
luminous flame of a blast-lamp, while a current of air is blown 



ORGANIC ANALYTICAL METHODS 87 

from a blast into the bottom of it by means of a narrower, longer 
(10 cm.) tube inserted in the larger tube; this operation is con- 
tinued until all moisture is removed. Or the combustion tube is 
clamped in a horizontal position, a narrower tube extending to 
the sealed end, attached to suction, is inserted, and the combustion 
tube equally heated with a Bunsen burner throughout its entire 
length ; the water vapour is drawn off by the suction. To reduce the 
long copper spiral which is to be used for the reduction of oxides 
of nitrogen which may be formed, the method of procedure is as 
follows : Into a test-tube large enough to admit the spiral, 1 c.c. of 
methyl alcohol is placed ; the spiral, held by crucible tongs, is then 
heated to glowing in a large, somewhat roaring blast-flame, and 
dropped as quickly as possible into the test-tube ; since this be- 
comes strongly heated at its upper end, it is clamped in a test-tube 
holder, or wrapped in a cloth or strips of paper. The dark spiral 
soon assumes a bright metallic lustre, while vapours, having a sharp, 
pungent odour (oxidation products of methyl alcohol like formic 
aldehyde and formic acid), which frequently become ignited, are 
formed ; after a few minutes, the tube may be loosely corked, and 
the spiral allowed to cool. When this operation is ended, the cop- 
per oxide will have been sufficiently heated, and the flames may be 
removed. During the cooling, the substance to be analysed is 
weighed. A convenient method is this : The weight of the weigh- 
ing-flask is determined with exactness to centigrammes, this weight 
is entered in the note-book at a convenient place for future use. 
The substance to be analysed is now placed in the weighing-tube, 
and the weight of the tube, plus substance, is determined exactly 
to the tenth of a milligramme. In the meantime, the copper 
oxide has cooled sufficiently to be transferred to the appropriate 
flask. The combustion tube is next filled. 

Filling the Tube. — At the edge of the working table is placed 
a stand ; fastened firmly near the bottom of this is a clamp pro- 
jecting over the edge of the table supporting the combustion tube 
in a vertical position, the mouth being at about the level of the 
table. The tube is now directly filled with the magnesite until 
the layer has a height of 10-12 cm. (Fig. 54). A small roll of 



88 



GENERAL PART 



5 cm. free 
10 cm. reduced copper spiral 



> 30 cm. coarse oxide 



copper gauze 1-2 cm. long, held with pincers or tongs, is heated 
for a short time in a Bunsen flame (it need not be reduced) and 
dropped on the magnesite. The funnel-tube is then placed in 
the tube, and from the flask coarse copper oxide is poured in until 
the layer measures 8 cm., and upon this is poured a layer of 2 cm. 
of the fine oxide. To the operation following — the mixing of the 

substance with copper oxide 
and the transference of the 
mixture to the tube — especial 
care must be given. In the 
bottom of a small mortar, 
standing on black, glazed pa- 
per a \ cm. layer of the fine, 
perfectly cooled copper oxide 
is placed ; to this is added from 
the weighing- tube the sub- 
stance to be analysed, of which 
0.15-0.20 gramme is taken, 
unless the substance contains 
a small proportion of nitrogen, 
when more is taken. Since 
the weight of the empty tube 
is known as well as that of 
the substance contained there- 
in, one can easily decide, by 
measuring with the eye, how 
much of the substance to 
take. Fine copper oxide is 
now added until the substance 
is completely covered, and the 
two are carefully mixed by 
stirring with the pestle, without pressure ; during the mixing care 
must be taken not to stir so rapidly as to cause dust-like particles 
of the mixture to leave the mortar. With the aid of a clean, 
clipped feather, such as is used in quantitative operations, or a 
small brush, the contents of the mortar are transferred through 



H 



10 cm. substance + fine oxide 



- 2 cm. fine oxide 



cm. coarse oxide 



2 cm. copper spiral 



12 cm. magnesite 



FIG. 54. 



ORGANIC ANALYTICAL METHODS 89 

the funnel-tube into the combustion tube. The operation must be 
done cautiously to prevent the light, dusty particles from being 
blown away. The mortar, as well as the pestle, is now rinsed 
with a fresh portion of the fine copper oxide, and this is likewise 
transferred to the tube with the aid of the feather. The layer of 
substance plus copper oxide should be about 10 cm. long. Then 
follows a layer of 30 cm. of coarse copper oxide, and finally the 
reduced copper spiral. 

The length of the tube, as well as that of the single layers, is 
regulated in accordance with the size of the combustion furnace; 
the figures given above refer to a furnace possessing a flame surface 
of 75 cm. Generally the tubes are 5 cm. longer than the furnace ; 
the tube contents are of the same length as the flame surface. 

Heating the Tube. — After the tube is filled it is held in a hori- 
zontal position and tapped gently on the table in order that a 
canal may be formed in the upper portion of the fine copper 
oxide ; it is then connected with a rubber stopper to the absorp- 
tion apparatus which has been charged with caustic potash solution, 
and placed in the combustion furnace, the rear end of which (that 
under the magnesite) has been raised on a block (Fig. 55). The 
following points are to be observed : In the lower part of the 
absorption apparatus there must be a sufficient amount of mercury 
to extend almost to the side-tube ; if this is not the case, more mer- 
cury is added : the end of the glass tube passing through the 
rubber stopper must be flush with the end of the stopper. In 
order to protect the latter from the heat, there is placed over the 
portion of the tube projecting beyond the furnace, an asbestos 
plate having a circular opening in the centre. After opening the 
pinch-cock of the absorption apparatus, the burners under the last 
half of the magnesite are lighted ; the flames, being small at first, 
are increased in size, as soon as the tube becomes warmed, but not 
sufficiently to cause them to meet above the tube. In order to 
raise the temperature higher when it becomes necessary, the tube 
is covered from both sides with the tiles. After about ten minutes 
a rapid current of carbon dioxide is evolved, the magnesite being 
decomposed by heat as represented in the following equation : 
MgC0 3 = MgO + CQ 2 . 



90 



GENERAL PART 




ORGANIC ANALYTICAL METHODS 9 1 

During this operation the glass stop-cock of the absorption appa- 
ratus is opened, and the pear-shaped vessel placed as low as pos- 
sible, so that it contains the principal portion of the caustic potash. 
After a rapid current of carbon dioxide has been evolved for about 
fifteen minutes, the burners under the copper spiral are lighted 
in order to drive out any occluded gas (hydrogen), the pear- 
shaped vessel is raised high enough to cause the caustic potash 
to ascend somewhat above the tubulure in the glass cock, the 
latter is closed, and the pear-shaped vessel again lowered as far 
as possible. When the air in the tube has been completely 
replaced by carbon dioxide, only a minimum quantity of light 
foam should collect over the potash in the course of two minutes. 
If this is not the case, and a large air volume collects, the glass 
cock is opened, upon which the potash flows in to the lowered 
pear vessel, and carbon dioxide is caused to pass through the 
tube for five minutes longer. The pear vessel is then raised as 
high as at first, the glass cock closed, and the former lowered. An 
observation will show whether the air has been displaced, which 
should be the case under normal conditions. If now after two 
minutes only a trace of foam has collected, the end of the delivery 
tube is dipped under the water in a dish as shown in Fig. 55, the 
pear raised to the highest point of the delivery tube, and the glass 
cock opened in order that the potash may drive out the air in the 
delivery tube : when this has been done, the cock is closed again 
and the pear lowered to the bottom. All the flames but one 
under the magnesite are now extinguished or lowered, and those 
under the long copper spiral as well as those under four-fifths of 
the adjacent layer of coarse copper oxide are lighted at the same 
time ; the flames, small at first, are increased in size, after the tube 
has become somewhat heated, until the copper oxide is heated 
to dull redness. Concerning the steps taken in heating the tube, 
refer to Fig. 54 — the numbers on the left indicate the portions of 
the tube to be heated successively. At this point care is taken 
that the flames are not so large as to meet above the tube. As 
before in heating the magnesite, after the first warming the heated 
portions of the tube are covered on both sides with the tiles. As 
soon as the forward layer of coarse copper oxide becomes dark 
red, the burners under the rear layer of coarse oxide adjacent to 



92 GENERAL PART 

the magnesite are lighted — small flames at first, which are increased 
after a time, the tube being covered simultaneously with the tiles. 
Care must be taken that the flames nearest the layer of substance 
plus fine copper oxide are not too large, in order that the substance 
may not yet be burned. Upon the operation which now follows — 
the gradual heating of the fine oxide containing the substance — 
virtually depends the success of the analysis. For the proper 
manipulation of this operation especial care must be taken. It is 
a rule that the heating had better be somewhat too slow than too 
rapid. A small flame is now lighted at the point adjacent to the 
short layer of coarse oxide : an observation of the absorption appa- 
ratus will show whether after some time any unabsorbed gas collects. 
If this is the case, no other burners are lighted until the evolution 
of gas ceases. When the gas no longer collects, another burner 
on the opposite side of the fine oxide is lighted. In this way the 
burners are gradually lighted from both sides, toward the middle 
of the fine oxide, and after, in each case, the cessation of the 
evolution of the gas, the flames are gradually made larger until 
finally the tube covered with tiles is heated with full flames ; thus 
the substance is regularly and quietly burned. The combustion 
must be so conducted that the bubbles of gas ascend in the absorp- 
tion apparatus with a slow regularity. If the single bubbles cannot 
be counted, or if they are so large as to occupy almost the entire 
cross-section of the absorption tube, the heating is too strong, and 
the last burners lighted must be extinguished or lowered, the tiles 
being also laid back at the same time if necessary, until the gener- 
ation of the gas is lessened. When this is ended, small flames are 
again lighted under the entire layer of magnesite, and increased in 
size after some time. As soon as the evolution of carbon dioxide 
has become active, the flames under the rear half of the magnesite 
lighted at the beginning of the analysis are extinguished. After a 
rapid current of carbon dioxide has passed through the tube for 
ten minutes, all the nitrogen is carried over to the absorption 
apparatus. This is shown by the complete absorption of the gas 
bubbles by the potash, as at the beginning of the analysis, except 
for a minimum foam-like residue. The absorption apparatus is 



ORGANIC ANALYTICAL METHODS 



93 



then closed by the pinch-cock and the rubber stopper bearing the 
connecting tube is withdrawn from the combustion tube. The gas 
is not immediately transferred to the eudiometer, but the pear is 
raised until the surfaces of the liquid in the pear and that in the 
tube are at the same level : the apparatus is then allowed to stand 
for at least half an hour. The flames under the combustion tube 
are not turned out simultaneously, but first one is extinguished, 
and then after a short time another, and so on. During the cool- 
ing of the tube the weighing-flask is weighed again. 

Transferring the Nitrogen. — After the nitrogen has stood in 
contact for at least half an hour with the caustic potash, in order 
that the last portions of carbon 
dioxide may be absorbed, the 
end of the delivery tube is dipped 
under the surface of the water 
contained in a wide-mouth cylin- 
der, as represented in Fig. 56, 
care being taken that in the 
lower bent portion of the de- 
livery tube no air bubbles are 
present ; if there are, they must 
be removed with a capillary 
pipette. The eudiometer is now 
filled with water, the end closed 
with the thumb, inverted and 
dipped below the surface of the 
water, the thumb removed and 
the tube clamped to the cylinder, at an oblique angle, so that the 
end of the delivery tube may be passed under it. The pear 
supported by the clamped ring is raised as high as possible above 
the delivery tube, and the glass cock gradually opened. The 
nitrogen is thus transferred to the eudiometer, the cock being 
left open until the delivery tube is completely filled with the 
caustic potash. The absorption apparatus is then removed, the 
eudiometer wholly immersed in the water. To obtain the tem- 
perature, a thermometer, held in the clamp which supported the 




Fig. 56. 



94 GENERAL PART 

delivery tube, is immersed in the water as far as possible. After 
about ten minutes, the nitrogen has come to the same tempera- 
ture as the water, the eudiometer is then seized with a clamp 
especially adapted to this purpose, or crucible tongs, — never with 
the hands, — and is raised so far out of the water that the level 
of water inside and outside the tube is the same. The volume of 
gas thus read off, is under the same pressure as that indicated by 
a barometer. 

Calculations of the Analysis. — If s is the amount of substance 
in grammes, v the volume of nitrogen read at the temperature t°, 
and b the height of the barometer in millimetres, w the tension 
of the water vapour in millimetres at /°, then the percentage of 
nitrogen is p : 

_ v-{b — w)- 0.1256 

~~ 760- (1 + 0.00367- t)-s 

The calculation of the analysis is rendered easier by referring to 
the table in which the weight of one cubic centimetre of moist 
nitrogen is given in milligrammes at different temperatures and 
pressures. If this, under the observed conditions, is g, then the 
percentage of nitrogen is : 

p= *. 

s 

In this formula, s is the weight of the substance in milligrammes. 

Length of Time for an Analysis. — The following abstract will 
give an approximate idea of the length of time that the single 
operations of a well-conducted combustion ought to occupy. 
From the beginning of the heating of the magnesite to the ap- 
pearance of a rapid current of carbon dioxide requires about 
10 minutes, the first test as to whether air is still present in the 
tube follows after a further 15 minutes ; length of time for various 
tests, 5 minutes. From the warming of the forward layer of the 
copper oxide with the spiral to the heating of the rear layer of 
oxide to a dark red heat, 15 minutes. The actual combustion 
of the substance requires 30 minutes. The displacement of the 
last portions of nitrogen by heating the magnesite requires 10 
minutes. Total, 1 hour and 25 minutes. 



ORGANIC ANALYTICAL METHODS 



95 



These time figures are, of course, only to be considered as 
approximate, since they depend upon the efficiency of the fur- 
nace, upon the nature of the substance burned, upon the skill 
of the experimenter, and upon other factors. 

WEIGHT OF ONE CUBIC CENTIMETRE OF MOIST NITROGEN 
IN MILLIGRAMMES. 1 



/ 


b. 726 


728 


730 


732 


734 


736 


738 


740 


5° 


1. 168 


1.171 1 


175 


1.178 


1. 181 


1. 184 


1.188 


1. 191 


6° 


1. 163 


1. 167 1 


I70 


1. 173 


1. 176 


1-179 


1.183 


1. 186 


7° 


1. 158 


1. 162 1 


I6 5 


1. 168 


1. 171 


I-I74 


1. 178 


1.181 


8° 


1153 


1157 1 


l6o 


1.163 


1.166 


1. 169 


*'i73 


1. 176 


9° 


1. 148 


1.152 1 


155 


1.158 


1. 161 


1. 164 


1.168 


1. 171 


IO° 


1 143 


1. 147 1 


I50 


"53 


1. 156 


I.I59 


1. 163 


1. 166 


n° 


1.138 


1. 142 1 


*45 


1. 148 


1. 151 


i-i54 


1. 158 


1. 161 


12° 


I-J33 


1-136 1 


140 


1. 143 


1. 146 


1149 


1. 152 


1.155 


13° 


1. 128 


1.131 1 


135 


1.138 


1. 141 


1. 144 


1. 147 


1-150 


i 4 ° 


1-123 


1. 1 26 1 


129 


1. 133 


1. 136 


I-I39 


1. 142 


I-I45 


15° 


1.118 


1. 121 1 


124 


1. 127 


1-131 


1.134 


1137 


1. 140 


1 6° 


1.113 


1.116 1 


119 


1. 122 


1. 125 


1. 129 


1. 132 


1.135 


17° 


1.108 


1. in 1 


114 


1. 117 


1. 120 


1-123 


1. 126 


1-130 


1 8° 


1. 102 


1-105 1 


109 


1. 112 


1. 115 


1. 118 


1. 121 


1. 124 


19 


1.097 


1. 100 1 


103 


1. 106 


1. no 


1.113 


1. 116 


1. 119 


20° 


1.092 


1.095 T 


098 


I.IOI 


1. 104 


1. 107 


1. no 


1.113 


21° 


1.086 


I.089 J 


092 


1.096 


1.099 


1. 102 


1. 105 


1. 108 


22° 


1. 08 1 


I.084 I 


087 


1.090 


1.093 


1.096 


1.099 


1. 102 


23 


i.o75 


I.O78 I 


081 


1.084 


1.088 


1. 09 1 


1.094 


1.097 


24° 


1.070 


I.O73 I 


.076 


1.079 


1.082 


1.085 


1.088 


1. 09 1 


25° 


1.064 


I.067 * 


070 


1-073 


1.076 


1.079 


1.082 


1.085 


26° 


1.058 


I. o6l I 


064 


1.067 


1.070 


1-073 


1.076 


1.079 


27 


1.053 


I.O56 I 


059 


1.062 


1.065 


1.068 


1. 07 1 


1.074 


28° 


1.047 


I.050 I 


053 


1.056 


1.059 


1.062 


1.065 


1.068 


29 


1. 041 


I.O44 I 


047 


1.050 


1.053 


1.056 


1-059 


1.062 


3o° 


1-035 


I.O38 I 


041 


1.044 


1.047 


1.050 


1.053 


1.056 



1 The values for fractions of degrees and for die height of the barometer not 
given in the table may be obtained by interpolation. 



96 



GENERAL PART 



o 

t^ 

00 
vO 
t^ 

vO 

VO 

r^ 

VO 

CM 

vO 


o ■«*■ On <+ On tJ- 

tJ- co CM CM »-l HH 
CM CM CM CM CM CM 


CO COCO CM *->. 

o o on onoo 

CM CM M hh M 


CM VO HH LO O 

oo r^ t^vo vo 


TJ-00 CM t^HH 
LO rj- ^f CO CO 


LOON COVD O 

CM HH HH O O 


vO w VO i-i vO O 
ro co 0) CM hh m 
CM CM CM CM CM CM 


lo O lo on -^h 

O O OnOO 00 


CO COCO CM VO 
r^ t^-vO vO lo 


HH lo ON -rJ-00 
lo Tf CO CO CM 


CM vO O co l>» 

CM HH HH o ON 











cooo coco CM t^ 

CO 01 CM M M O 
CM <N M CM CM CM 


O On ONOO CO 

OJ M fl HH M 


lo O -st" On CO 
i>. r^vo lo lo 


00 CM VO hh lo 
Th ^ CO CO CM 


On co t^ O ^h 

i hh O O On 

HH HH HH HH O 


O lo O rh On tJ- 
ro CM M h. O O 
CM CM CM CM CM CM 










NNVO hvO m 

CM CM M w o O 

M M N N N N 


On OnOO 00 t-^ 


On ^00 CO f^ 

vo vO lo lo rj- 


CM VO O ^ On 
tj- CO CO CM hh 


fONH LOCO 

hh o O OnOO 

HH HH HH O O 












v§ 

oo 

t^ 

vO 

LO 
t^ 

^1- 
LO 

CM 

LO 


cooo cooo cooo 
CM hh hh O O On 
CM CM CM N CM HH 










O lo o ^o O rh 

CM hh _, O O On 
M CM CM M CM hh . 


On Tt" On ^00 

00 00 t— r^-vO 


CO00 CM- t-^ hh 

VO LO LO *J" ^ 


lo O ^00 CM 

co CO CM HH HH 


t^ M LO ON CM 

O O OnOO 00 










t^. CM NNVO M 
M M O O On On 

CM CM IN CM HH HH 










Tt- On COCO COCO 
hh O O On ONOO 
CM CM CM hh hh hh 


CO00 CM t^ CM 
OO t^ r^vO vO 


t^ HH "O O LO 

lo lo ^f Th co 


On ^-00 CM vO 

CM CM HH HH O 


HH LO on covO 

O onoo oo t> 

hh O O O O 


O lo o lo O lo 

m O O On OnOO 
NNMhmm 




















o 

LO 

00 
VO 

CM 

rt- 

!>. 


t^ CM t^ CM r-^ CM 

O O On ONOO 00 

CM CM IH 1-1 1-H l-H 


NHVfl MVO 

^ t^vO vO lo 


O lo O ^ On 
LO t*- Tf CO CM 


COOO CM vO O 

CM HH HH O O 


lo On co t~>. O 

ONOO OO NN 

o o o o o 


Tt" On ^t" On t}-CO 
O On OnOO 00 I s * 

CM _ _ hh HH hH 






■"! M . M . H . °. 


o o o o o 


1-1 VO HH VO O VO 

O On OnOO 00 r^ 

CM 1- w M 1-1 M 


O lo O lo On 
r^vO vO lo t}- 


tJ- On COOO CO 
Tj- co CO CM CM 


NhvOO ^t 

HH HH o O ON 
11 M HH ^ O 


ON CO t^ HH LO 

OOOO N l>.VO 

o o o o o 


t~s. CM i>. CM !>. CM 

ON ONOO 00 NN 










rf- On tJ- On tj- On 
OnOO 00 t~-» I>-vO 


tJ- On CO00 co 

NO LO LO ^ rj" 


00 CO f^ CM vO 
CO CO CM CM hh 


HH LO O ^"00 
HH O O ONOO 
HH HH HH O O 


co r^ hh lo On 
oo t^» r^vo lo 

o o o o o 












Ts> 


O O O O O O 
lovO t>>00 On O 




HH HH HH HH CM 


CM CM CM CM CM 


CM CM CM CM CO 



ORGANIC ANALYTICAL METHODS 97 

Subsequent Operations. — After the tube has cooled and the 
copper spiral taken out, all the copper oxide is sifted to separate 
the coarse from the fine, and may be used again for further 
analyses as often as desired, provided that it is reheated each 
time in the nickel crucible to oxidise it. The tube may also be 
used again if it has not been distorted by high heating. The 
magnesite is useless for further analyses. 

The caustic potash in the absorption apparatus, which can be 
used a second time, is poured into a bottle, which is then well 
closed. The absorption apparatus, including the rubber tubing, is 
washed out repeatedly with water, so that the latter may not be 
corroded by the caustic potash. 

General Remarks. — The above-described method of Dumas 
for nitrogen is used in variously modified forms, but the principle 
is the same in all. It is preferred in many places to generate the 
carbon dioxide from acid sodium carbonate or manganese car- 
bonate. A combustion tube open at both ends may be used, if a 
number of nitrogen determinations are to be made. The tube 
is charged as represented in Fig. 60 (page 103). The substance 
is placed in a porcelain or copper boat. In order to replace the 
air by carbon dioxide, the rear end of the tube is connected with 
another tube of difficultly fusible glass (closed at one end), 25-30 
cm. long and 15-20 mm. wide, which is three-fourths filled (in 
cross section) with sodium bicarbonate. In order to absorb the 
water generated from this on heating, a small sulphuric acid wash 
bottle is interposed between the two tubes. The layer of bicar- 
bonate is heated with a single Bunsen burner, beginning at the 
fused end. In order to protect the bicarbonate tube from the 
direct flame, it is surrounded by a cylinder of coarse iron gauze 
(Fig. 5 7) . The bicarbonate may be replaced by a Kipp generator. 

Further, the mixing of the substance with the fine copper oxide 
may be done in the tube. Instead of the absorption apparatus 
of Schiff, described above, a graduated tube from which the vol- 
ume of the gas may be read directly may be used, thus obviating 
the necessity of transferring it to a eudiometer. This modifica- 
tion carries with it, however, the disadvantage that the tension of 

H 



98 GENERAL PART 

caustic potash is not exactly known, and therefore a somewhat 
arbitrary correction must be applied. But as mentioned these 
modifications do not differ essentially. 




Fig. 57. 

QUANTITATIVE DETERMINATION OF CARBON AND HYDROGEN 
LIEBIG'S METHOD 

The essential part of the method consists in completely burning 
with copper oxide a weighed amount of the substance, and then 
weighing the combustion products, carbon dioxide and water. 

The requisites for analysis are : 

1. A hard glass tube open at both ends; outside diameter 12- 

15 mm. It should be about 10 cm. longer than the furnace. 

2. Four hundred grammes of coarse and 50 grammes of fine 

copper oxide, preserved in bottles closed with tin-foil- 
covered corks as in the nitrogen determination. But the 
copper oxide used for the latter purpose and that for the 
carbon and hydrogen determinations are always kept in 
separate bottles. 

3. A U-shaped and a straight calcium chloride tube. 

4. A caustic potash apparatus. The Geissler form is the most 

convenient. 

5. A drying apparatus for air or oxygen. 

6. Two one-hole rubber stoppers fitting the ends of the com- 

bustion tube. 

7. A glass tube provided with a cock. 

8. Two copper spirals of 10 and 12-15 cm. length, respectively; 

two short spirals 1-2 cm. long. 



ORGANIC ANALYTICAL METHODS 99 

9. A piece of good rubber tubing 20 cm. long ; six pieces rubber 
tubing 2 cm. long (thick-walled and seamless). 

10. A porcelain and a copper boat. 

11. A screw pinch-cock. 

12. Two asbestos plates for the protection of the rubber stoppers. 

Preparations for the Analysis. — The sharp edges of the com- 
bustion tube are rounded by careful heating in a blast-flame. After 
cooling the tube is rinsed out with water several times ; this is 
allowed to drain off, and the tube dried by one of the methods 
given on page 70. 

The coarse copper oxide is not previously heated in the nickel 
crucible as in the determination of nitrogen, but this is done later 
in the tube itself. If the nature of the substance to be analysed 
is such that it is necessary to mix it with fine copper oxide, the 
latter is ignited for a quarter hour in the porcelain crucible and 
allowed to cool in a desiccator. 

The U-tube for the absorption of the water (Fig. 61) is filled 
with granulated, not fused, calcium chloride, which must be freed 
from any powder by sifting. In order to prevent the calcium 
chloride from falling out, both ends of the tube are provided with 
loose plugs of cotton. The open leg is closed by a rubber stopper 
or a good cork bearing a glass tube bent at a right angle. The 
cork stopper is covered with a thin layer of sealing-wax. Calcium 
chloride tubes, in which the open leg is longer than the other, are 
very convenient. After the tube is filled the open end may be 
sealed in a blast-flame. In this case the plug in this end is not 
cotton, but asbestos or glass-wool. In order that the tube may 
be suspended from the arm of the balance in weighing, a platinum 
wire with a loop in the centre is attached to both legs. Calcium 
chloride often contains basic chlorides, which not only absorb 
water, but also carbon dioxide, thus causing an error in the results 
of the analysis ; before the filled tube is used a stream of dry 
carbon dioxide is passed through it for about two hours, dried air 
is then drawn through for half an hour to displace the carbon 
dioxide. The two side tubes of the calcium chloride tube are 



:oo 



GENERAL PART 



closed by pieces of rubber tubing 2 cm. long, in which is inserted 
a glass rod rounded at both ends, i|- cm. long. The tube may 
be used repeatedly until the calcium chloride begins to liquefy. 
The straight calcium chloride tube is filled in like manner, but it 
is unnecessary to pass carbon dioxide through this before using. 

The three bulbs of the potash apparatus similar to the one 
represented in Fig. 58 are three-fourths filled with a solution of 
caustic potash (2 parts potassium hydroxide, 3 parts water) as 
follows : the horizontal tube which is to be charged with solid 
caustic potash is removed, and to the free end of the bulb tube 
rubber tubing is attached. The inlet tube represented in Fig. 58 




Fig. 58. 

at the left is now dipped into the caustic potash solution, con- 
tained in a shallow dish, and this is sucked up with the rubber tub- 
ing until the three bulbs are three-fourths filled. Care must be 
taken not to suck too strongly, otherwise some of the caustic potash 
solution may be drawn into the mouth. This may be prevented by 
inserting an empty wash-bottle between the potash apparatus and 
the mouth, or the suction-pump may be used, in which case the 
water-cock must be opened to a very slight extent. After filling 
the bulbs that part of the tube immersed in the potash solution 
is cleaned with pieces of rolled-up filter-paper. The horizontal 
potash tube, removed before filling the bulbs, is now filled with 



ORGANIC ANALYTICAL METHODS IOI 

coarse-grained soda-lime and solid caustic potash in pea-size 
pieces as follows : In the bulb is placed a plug of glass-wool or 
asbestos, then follows a layer of the soda-lime, a layer of caustic 
potash, and finally another plug of glass-wool or asbestos. When 
this is done, it is closed in the same way as the calcium 
chloride tube. In handling the Geissler tubes it is always to be 
remembered that they are very fragile, and in all cases the lever- 
arm formed in lifting them should be as short as possible. When 
the apparatus is to be closed by rubber tubing, e.g., it is not 
grasped by the bulbs, but immediately behind the place over 
which the tubing is to be drawn or pushed. When the potash 
apparatus has been used twice, it must be refilled. The longer of 
the two so-called copper oxide spirals need not be reduced before 
the combustion ; on the contrary, it is oxidised in the combustion 
tube, as will be pointed out below. In order to be able to remove 
it from the tube conveniently a loop of copper wire is fastened in 
the meshes of the gauze near the end, or a not too thin copper 
wire is passed through the centre of the spiral and bent at one 
end to a right angle and at the other in the form of a loop. The 
shorter spiral, which, as in the nitrogen determination, serves to 
reduce any oxides of nitrogen, is next reduced according to the 
directions given on page 87. To remove any adhering organic 
substances like methyl alcohol or its oxidation products the spiral 
is placed, after cooling, in a glass tube 20 cm. long, one end of 
which is narrowed ; carbon dioxide is passed through it, and as 
soon as the air has been displaced, it is heated for a few minutes 
with a Bunsen flame and then allowed to cool in a current of car- 
bon dioxide. To remove the mechanically adhering gas the spiral 
is placed in a vacuum desiccator. If this is not at hand, an ordi- 
nary desiccator containing a small dish of solid caustic potash or 
unslaked lime is used. (It may also be heated in an air-bath at 
ioo-no .) 

For drying the oxygen or air an apparatus consisting of two wash 
cylinders and two U-shaped glass tubes mounted on a wooden 
stand is employed. The gas passes first through a wash cylinder 
containing a solution of potassium hydroxide (1 : 1), then a tube 



102 



GENERAL PART 



filled with soda-lime, then one filled with granulated calcium chlo- 
ride, and finally a wash cylinder containing sulphuric acid (Fig. 59). 
The legs of the glass tube containing the stop-cock are fused 
off and slightly narrowed at the ends, so that on either side of the 
cock the length is 5 cm. 

Filling the Tube. — The simplest case of combustion with which 
one can deal is that involving the analysis of a substance contain- 
ing no nitrogen. In a case of this 
kind, assuming that the furnace has a 
flame surface of 75 cm., the tube is 
filled in the following manner : A short 
copper gauze roll, 1-2 cm. long, of suf- 
ficient diameter to fit the tube tightly, 
and somewhat elastic, is pushed into 
the tube 5 cm., and then the opposite 
side of the tube is partially filled with a 
layer of coarse copper oxide 45 cm. 
held in position by another small elastic 
copper spiral at its upper end. Into 
the tube lying in a horizontal position 
the copper oxide spiral is pushed so 
far that its loop is 5 cm. from the 
mouth of the tube (Fig. 60). 
Igniting the Copper Oxide. — The charged tube is placed in the 
furnace, the end nearest the copper oxide spiral is closed by a 
rubber stopper bearing the glass stop-cock tube, and the latter is 
connected with the drying apparatus by means of rubber tubing 
provided with a screw pinch-cock. The other end of the tube 
is allowed to remain open at first ; while a current of oxygen is 
passed through the tube, slow enough to enable one to count the 
bubbles (the glass stop-cock is opened wide and the current regu- 
lated with the pinch-cock), the entire length of the tube is heated, 
at first with flames as small as possible ; these are gradually in- 
creased until finally, the tiles being in position, the copper oxide 
begins to appear dark red. The water deposited at the beginning 
of the heating, in the forward cool end of the tube, is now removed 




Fig. 59. 



103 



5 cm. free 
) Short copper spiral 



45 cm. coarse oxide 



Short copper spiral 
io cm. free 



15 cm. copper oxide 

spiral 



5 cm. free 
FIG. 60. 




104 GENERAL PART 

with filter paper wrapped around a glass rod. When no more 
water collects, the front end of the tube is closed by a rubber 
stopper bearing the straight calcium chloride tube. After about 
20 or 30 minutes' heating the burners under the copper oxide 
spiral, the adjacent empty space, and those under about 5 cm. of 
the copper oxide layer lying next, are extinguished, and at the 
same time the current of oxygen is cut off. 

Weighing the Absorption Apparatus and the Substance. — While 
the rear part of the tube is cooling, the calcium chloride tube, the 
potash bulbs, and the substance are weighed. Before the absorp- 
tion apparatus is weighed, it is wiped off with a clean cloth, free 
from lint, and the rubber tubing and glass rods removed ; after the 
weighing, these are replaced. The substance, if solid, is weighed 
in a porcelain boat which has previously been heated strongly, and 
cooled in a desiccator. The boat is first weighed empty, 0.15 to 
0.20 grammes of the substance placed in it and weighed again; it 
is then placed on a tin-foil-covered cork, in which a suitable groove 
has been cut, and transferred to a desiccator. 

The Combustion. — When the rear end of the tube is cold, the 
copper oxide spiral is withdrawn with a hooked glass rod or wire, 
the porcelain boat is inserted as far as the coarse copper oxide, 
care being taken not to upset the boat, and finally the spiral is 
replaced. The stop-cock tube, with the cock closed, is then put 
in position. The straight calcium chloride tube is replaced by 
the weighed U-tube, with its empty bulb, which will condense the 
greater portion of the water, nearest the furnace. To the U-tube 
is connected, by a rubber joint, the potash apparatus, and the 
soda-lime tube of the latter with the straight calcium chloride 
tube in the same way (Fig. 61). The connecting of the different 
parts of the apparatus may be facilitated by blowing air from the 
lungs through each rubber joint before pushing it on the glass 
tubes. Especial care is taken to have a good joint between 
the U -calcium chloride tube and the potash bulbs, since at this 
point very commonly lies the source of error in analyses not con- 
cordant. A thick-walled seamless rubber tubing is employed ; 
it is drawn over the two ends of the glass tubes until they touch. 



ORGANIC ANALYTICAL METHODS 105 

In order to provide against any possible leak, two ligatures of thin 
copper wire or "wax ends" are bound around the joints. A test 
as to whether the apparatus is perfectly tight is not always con- 
vincing when the combustion is conducted in an open tube ; since, 
on the one hand, the heating is not constant, and on the other, 
in consequence of the friction of the solution in the narrow tubes, 
a leak, at times, may not be detected. The rubber stoppers 
closing the tube may be protected from the heat by placing on 
the tube, close to the furnace, an asbestos plate with a circular 
hole in the centre. After closing the screw pinch-cock, the glass- 
cock is opened, and a slow current of oxygen (two bubbles per 
second) is admitted to the tube by carefully opening the pinch- 
cock. Small flames are now lighted under the copper oxide 
spiral, which are increased after some time, until, finally, the spiral 
is brought to a dark red glow. When this is done, the flames 
under the unheated copper oxide are gradually lighted, care being 
taken not to allow any flame near the porcelain boat to be too 
large. Now follows the most difficult operation of the analysis, 
upon which the success of it virtually depends, viz. the gradual 
heating of the substance. This is conducted in exactly the same 
way as that given under the nitrogen determination. The heating 
is begun, at first, with a single small flame ; this is gradually in- 
creased in size, or several others may be lighted, then the tube is 
covered on one side with the tiles, and after a short time, on the 
other, and finally the full flames are used. With easily volatile 
substances, the heating at the beginning is not done with the 
flame, but by covering that portion of the tube containing the 
boat with hot tiles, taken from the forward highly heated portion 
of the furnace. Numerous modifications have been applied to 
this most difficult part of the analysis, concerning which no satis- 
factory general directions can be given. A valuable rule is to 
conduct the heating in such a way that the gas bubbles passing 
through the potash apparatus follow one another with as slow a 
regularity as possible. If the passage of bubbles becomes too 
rapid, the heating is moderated. If, during the combustion, 
water should condense in the glass-cock, or in the rear, cold 



106 GENERAL PART 

portion of the tube, as it always does in the front end, it is 
removed by holding a hot tile under it, or by heating with a small 
flame. When the boat has been heated some time with the full 
flames, the combustion is considered to be ended. In order to 
drive the last portions of carbon dioxide and water from the tube 
into the absorption apparatus, a somewhat more rapid current of 
oxygen is passed through the tube, until a glowing splinter held 
before the opening of the straight calcium chloride tube is ignited. 
During this operation, the water, condensed for the most part in 
the front end of the tube, is also driven over into the calcium 
chloride tube, as above described. When this has been done, the 
rubber stopper is withdrawn from the front end of the combustion 
tube, care being taken to prevent the water in the calcium chloride 
tube from running out. To remove the oxygen in the absorption 
apparatus, a slow current of air which need not be dried is drawn 
through it for 1-2 minutes, with the mouth or suction. The 
apparatus is taken apart, closed up as above described, allowed 
to stand in the weighing-room for half an hour, and is then 
weighed. From the difference in the weights of the absorption 
apparatus before and after the combustion, the percentage of 
carbon and hydrogen is found from the following equations : 
I. (approximate) : 

Percentage of Carbon = — — — — > 

& Wt. Substance x n 

i C 

g CO" = ° 43573 ~ * 

_ f " , 2 Wt. H s O X 100 

Percentage of Hydrogen = 



Wt. Substance x 9 

TT 

log H~6 = *° 4576 ~ z 

II. (exact) : 

r ^ u Wt C0 * X 300 

Percentage of Carbon = 



'o x 



Wt. Substance x 1 1 



1 C 

s ca = °' 43573 ~ * 

_ ^ e __ , " Wt. H 2 x 202 

Percentage of Hydrogen = r= — p— — 5 

5 * h Wt. Substance x 18.02 

TT 

log j^ = 0.04960 - I 



ORGANIC ANALYTICAL METHODS 107 

Modifications of the Method. — In many cases instead of using 
oxygen for the ignition of the copper oxide, the same result may 
be obtained by using a current of air. The combustion may also 
be conducted in a current of air ; but when the substance is diffi- 
cult to burn, it is still necessary toward the end of the operation to 
pass oxygen through the tube for some time. As soon as a glow- 
ing splinter held at the end of the straight calcium chloride tube 
is ignited, the combustion is ended. The combustion may also be 
conducted without passing a current of air or oxygen into the tube 
at the beginning, in which case the glass stop-cock is closed. 
Under these conditions, as soon as the substance has been 
heated for some time with the full flames, toward the end of the 
operation the glass stop-cock is opened and a current of air 
or oxygen passed through the tube. Substances which burn with 
great difficulty can also be mixed with fine copper oxide in a 
copper boat (see below), and then burned in the same way in 
oxygen. 

Combustion of Substances containing Nitrogen. — Since in the 
combustion of nitrogenous compounds, the reduced copper spiral 
serving for the reduction of the oxides of nitrogen must be used, 
the combustion tube is charged somewhat differently in this case. 
The first copper roll is inserted in the tube, not 5 cm., but 15 cm., 
the space in front of it being reserved for the reduced spiral. 
Consequently the layer of coarse copper oxide is but 35 cm., and 
not 45 cm., in length. No change is made in the disposition of 
the copper oxide spiral. The ignition of the copper oxide is 
conducted exactly as above, except that a current of air is used. 
If, however, the ignition should be conducted throughout with 
oxygen, at the end of the operation this is displaced by air. The 
further operations are the same as those described above, except 
that the reduced copper spiral is put in position last — just before 
connecting the combustion tube with the absorption apparatus. 
In order to prevent the oxidation of the copper, the combustion 
proper is performed with the glass-cock closed, and oxygen is 
not admitted to the tube until at the end. As soon as the oxy- 
gen is admitted, the flames under the reduced copper spiral are 



108 GENERAL PART 

extinguished. The gas is passed through until it can be detected 
at the end of the apparatus as above described. In the 
combustion of substances which leave a charred, difficultly 
combustible, nitrogenous residue, it is necessary to burn them 
by mixing with fine copper oxide. Since the porcelain boats 
are generally too small to contain a sufficient quantity of this, 
a boat made of sheet copper, 8 cm. long and of a width suffi- 
cient to enable it to be just passed into the tube, is used. It 
is filled as follows : After it has been previously ignited, it is 
placed upon a sheet of black glazed paper, and half filled with 
fine copper oxide also previously ignited and afterwards cooled 
in a desiccator. Upon this is carefully spread the weighed sub- 
stance from a weighing-tube as in the nitrogen determination, 
then a layer of fine copper oxide is added until the boat is 
three- fourths full : the substances are now well mixed by care- 
ful stirring with a thick platinum wire. If some of the mixture 
should fall upon the glazed paper, it is returned to the boat with 
the aid of a feather or brush. The combustion is made with the 
glass-cock closed. Oxygen is not admitted until at the end of 
the operation. 

Combustion of Substances containing Sulphur or a Halogen. — 
Sulphur compounds cannot be burned with copper oxide in 
the manner described, since at a red heat the copper sulphate 
formed gives off sulphurous acid, which is absorbed by the 
potash apparatus along with the carbon dioxide, giving a result 
in which the percentage of carbon is too high. In this case 
the oxidation is accomplished with granulated lead chromate. 
The filling of both ends of the tube is done just as described 
above : copper oxide spiral, empty space for boat, long layer of 
lead chromate. The ignition in oxygen, etc., is also the same. 
But two points are here to be observed: (i) the lead chro- 
mate is not heated as strongly as the copper oxide, otherwise 
it fuses in the glass; and (2) the most forward portion of 
the lead chromate layer, nearest the calcium chloride tube 
(that above about three burners), is heated very slightly, since 
lead sulphate is not completely stable at a red heat. The sub- 



ORGANIC ANALYTICAL METHODS IO9 

stance is mixed in the copper boat with powdered, ignited lead 
chromate. 

Halogen compounds can be burned in the usual way with cop- 
per oxide ; but since the copper halides are partially volatile and 
give up the halogen on being heated to redness, a silver spiral 
must be inserted in the tube to retain the halogen. The tube is 
filled in the same way as for the combustion of a nitrogen com- 
pound, only in place of the reduced copper spiral, one of silver 
is used. But it is better to perform the combustion with lead 
chromate, in which case it will not be necessary to use a silver 
spiral. Since the lead halides are also somewhat volatile at a red 
heat, so, as above, the front part of the tube containing the lead 
chromate is heated but slightly. 

Combustion of Liquids. — If the compound to be analysed is a 

liquid, it can be weighed directly in the porcelain boat, provided 

it is very difficultly volatile. Moderately volatile substances are 

weighed in a small glass tube which is loosely closed with a glass 

stopper (see Fig. 53, page 76). In order to introduce this into 

the tube, it is placed in the porcelain boat in such a position that 

the mouth of the tube is directed upwards. A preliminary trial 

will show whether the boat containing the empty tube will pass 

into the combustion tube. Very easily volatile substances are 

weighed in small bulb-tubes which are sealed after weighing 

(Fig. 62). The filling is done as follows: The empty 

tube is weighed, heated gently, and the open end dipped 

under the liquid to be analysed. On cooling, the liquid 

will be drawn up into the bulb. If a sufficient quantity 

is not obtained the first time, the operation is repeated ; 

before it is sealed care must be taken that the capillary 

contains none of the liquid ; if it does, it must be removed 

by heating. It is now sealed, and the tube plus substance 

. Fig. 62. 

weighed. Care must again be taken to prevent any of the 

liquid from finding its way into the capillary, due to sudden 
movements or other causes. To prepare the tube for the com- 
bustion, the extreme end is filed and broken off, during which 
operation the tube is not held by the bulb. It is placed in the 



110 GENERAL PART 

boat with its open end elevated and directed toward the front 
end of the furnace. The precaution to ascertain beforehand 
whether the boat loaded with the tube will pass into the com- 
bustion tube, should always be taken. If necessary, the capillary 
is shortened. 

Calculation of the Atomic Formula. — In order to calculate the 
simplest formula of a substance from the figures giving its per- 
centage composition, the method is as follows : If a substance 
contains, e.g. : 

Carbon =48.98% 

Hydrogen = 2.72% 

Chlorine =48.30% 

the percentage figures are divided by the corresponding atomic 
weights. There is thus obtained : 

48.98-7-12 =4.08 C 

2.72 -r- I = 2.72 H 

48.30-^35-5 = i-3 6 CI 
These figures are divided by the smallest — in this case 1.36 : 
4.08 -r- 1.36 = 3 C 

2.72 -r- I.36 = 2 H 
I.36 -7- I.36 = I CI 

The simplest atomic formula, therefore, is C 3 H 2 C1. If the num- 
bers obtained in the last division are not integers, they are multi- 
plied by the smallest integer which will convert the fractions into 
whole numbers. If, e.g., the following numbers have been found, 
1.25, 1.75, and 0.5, they are multiplied by 4, the results being 
5, 7, and 2. 

The simplest formula thus obtained from the analytical data 
does not always correspond with the true molecular weight. This 
must be determined by one of the usual methods, unless it may 
be inferred from the nature of the reaction by which the sub- 
stance analysed was produced. 



ORGANIC ANALYTICAL METHODS III 

The exact atomic weights of the elements used in analytical 
calculations are : 



H = 


I.OI 


C = 


I2.00 


N = 


I4.O4 


S = 


32.06 


Cl = 


35-45 


Br = 


79.96 


I = 


126.85 



O = 16.00 

These figures are taken from the report of the Atomic Weight 
Committee of the German Chemical Society. 



SPECIAL PART 



1. REACTION 



I. ALIPHATIC SERIES 

THE REPLACEMENT OF AN ALCOHOLIC HYDROXYL 
GROUP BY A HALOGEN 



I. Example: Ethyl Bromide from Ethyl Alcohol 1 

To 200 grammes (no c.c.) of concentrated sulphuric acid con- 
tained in a round litre-flask, add quickly with constant shaking, 
without cooling, 90 grammes of alcohol (about 95%). After 
cooling the mixture to the room temperature, add carefully 75 
grammes of ice-water, the cooling being continued, and then 100 

grammes of finely pul- 
verised potassium bro- 
mide (see Hydrobromic 
Acid, page 345). The 
mixture is subjected to 
distillation, which must 
not be too slow, the flask 
being heated on a small 
sand-bath with a large 
flame (Fig. 63). Since 
the boiling-point of ethyl 
bromide is low (38 ), a 
Fig. 63. " long condenser, with a 

quite rapid current of water passing through it, is used. An up- 
right coil condenser (see Fig. 27, page 34) may be employed 
advantageously. At the beginning of the operation, the receiver 
is filled with a sufficient amount of water containing a few pieces 
of ice to allow the end of the adapter to dip under the surface. 
The reaction is ended as soon as the oily drops which sink to the 
bottom of the receiver cease passing over. If, during the distilla- 
tion, the contents of the receiver should be drawn up into the con- 
1 J. 1857,441. 112 




ALIPHATIC SERIES 113 

denser, this difficulty may be overcome by placing the receiver 
in such a position that the end of the adapter reaches just below 
the surface of the water. The same result may be attained by turn- 
ing the adapter to one side, so that air may enter it. The lower 
layer of the distillate consisting of ethyl bromide is washed in the 
receiver several times with water, and finally with a dilute solution 
of sodium carbonate, during which the flask must not be closed. 
The lower layer is then run out of a separating funnel, dried with 
calcium chloride, and finally distilled, the same precautions as to 
cooling, mentioned above, being observed. In this case, the free 
flame is not used for the heating, but the bulb of the fractionating 
flask is immersed in a vessel filled with water at 60-70 (compare 
page 22). The ethyl bromide distils between 35-40 , the main 
portion at 38-39 . In consequence of the low boiling-point of 
ethyl bromide, it is never allowed to stand in open vessels for any 
length of time ; during the drying over calcium chloride, the flask 
must be closed by a tight-fitting cork. The finished preparation, 
particularly at summer temperature, must not be preserved in thin- 
walled vessels of any kind, but always in thick-walled, so-called 
specimen bottles. Yield, 70-80 grammes. 

The ethyl bromide thus obtained is contaminated with a small 
amount of ether. If it be desired to prevent this, the well-cooled 
crude ethyl bromide, contained in a flask surrounded by a freezing 
mixture of ice and salt, is treated, before drying with calcium 
chloride, with concentrated sulphuric acid, added drop by drop 
and with frequent shaking, until it separates out in a layer under 
the ethyl bromide. The acid containing the dissolved ether is 
then run off (in a separating funnel) from the ethyl bromide, which 
is shaken up several times with ice water, dried with calcium chlo- 
ride, and redistilled as before. For the preparation of ethyl ben- 
zene (which see) the ethyl bromide thus purified cannot be used. 

2. Example: Ethyl Iodide from Ethyl Alcohol 1 

To a mixture of 5 grammes of red phosphorus and 40 grammes 
of absolute alcohol, contained in a small flask of about 200 c.c. 
capacity, 50 grammes of finely pulverised iodine are added gradu- 

1 A. 126, 250. 1 



114 SPECIAL PART 

ally in the course of a quarter hour ; the flask is frequently shaken 
during the addition, and cooled from time to time by immersion 
in cold water. An air condenser — a straight vertical glass tube 
is the common form — is connected with the flask, and the reac- 
tion mixture is allowed to stand at least four hours. (In case the 
experiment was begun late in the afternoon, it may stand until 
the next day.) In order to complete the reaction, the mixture is 
heated for two hours on the water-bath, a reflux condenser being 
attached to the flask. The ethyl iodide is then distilled off conven- 
iently by immersing the flask in a rapidly boiling water-bath. The 
distillation is facilitated by the use of a frayed thread (see page 34). 
Should the last portions go over with difficulty, the water-bath is 
removed, the flask is dried and heated for a short time with a 
luminous flame kept in constant motion. The distillate, coloured 
brown by iodine, is washed several times with water to free it from 
alcohol, and then with water to which a few drops of caustic soda 
have been added, to remove the iodine ; the colourless oil is now 
separated in a dropping funnel, dried with a small quantity of 
granular calcium chloride, and distilled. If the calcium chloride 
should float on the oil, it is poured through a funnel containing 
some asbestos or glass-wool into the fractionating flask. The boil- 
ing-point of ethyl iodide is 72 . Yield, about 50 grammes. 

Both of these reactions are special cases of a reaction of general 
application, viz. : the replacement of an alcoholic hydroxyl group with 
a halogen atom. This may be effected in two ways: (1) by causing 
the alcohol to react with the halogen hydracid as in the preparation 
of ethyl bromide, e.g. : 



C 2 H 5 . | OH + H| Br = H 2 + C 2 H 5 . Br 
(HC1, HI) 
(2) by treating the alcohol with a phosphorus halide, as in the prepara- 
tion of ethyl iodide, e.g. : 

3 C 2 H 5 .OH + PI 3 = 3C 2 H 5 .I + P(OH)3 
(PCL, PBr 3 ) 

1. The first reaction takes place most easily with hydriodic acid; in 
many cases saturation with the gaseous acid being sufficient to induce 
the reaction. Hydrobromic acid reacts with greater difficulty ; it is 



ALIPHATIC SERIES 115 

frequently necessary to heat the alcohol saturated with the acid in a 
sealed tube. The above method for the preparation of ethyl bromide 
is a simple case of the general reaction. In place of using hydrobromiC 
acid directly, it can in some cases, like the one given, be generated by 
warming a mixture of potassium bromide and sulphuric acid : 
KBr + H 2 S0 4 = HBr + KHS0 4 . 

Hydrochloric acid reacts with most difficulty, and it is, e.g., in the prepa- 
ration of methyl chloride and ethyl chloride, necessary to employ a 
dehydrating agent — zinc chloride is the best — or with the alcohols of 
high molecular weights, to heat in a closed vessel under pressure. 

This reaction is not only applicable to the aliphatic, but also to the 
aromatic alcohols ; e.g. : 

C 6 H 5 . CH 2 . OH + HC1 = C G H 5 . CH,C1 + H 2 

Benzyl alcohol Benzyl chloride 

But phenol hydroxyl groups cannot be replaced by the action of a 
halogen hydracid. 

With di-acid and poly-acid alcohols the reaction takes place, at least 
with hydrochloric and hydrobromic acids ; but, in this case, the number 
of hydroxyl groups which are replaced by the halogen depends upon 
the conditions of the experiment, the quantity of the halogen acid, the 
temperature, etc., e.g. : 

CH, . OH CH 9 . Br 

I + HBr = I + H 2 

CH 2 .OH CH 2 .OH 

Ethylene glycol Ethylene bromhydrine 

CH 2 .OH CH„.OH 

I I 

CH.OH +2HCI =CHC1 +2H 2 

! I 

CH 2 .OH CH,C1 

Glycerol Dichlorhydrine 

CH 2 .OH CH 2 .Br 

I I 

CH + 2 HBr = CH 2 + 2 H 9 

I I • 

CH 2 .OH CH 2 .Br 

Trimethylene glycol Trimethylene bromide 

Hydriodic acid, in consequence of its reducing properties, acts upon the 
poly-acid alcohols in a different manner. A single hydroxyl group, and 
that particular one in combination with a carbon atom which is in turn in 
combination with other carbon atoms, is replaced by iodine, while at times 
other hydroxyl groups are replaced by the hydrogen of the acid, e.g. : 



Il6 SPECIAL PART 

CH 2 .OH CH, 

I I 

CH . OH + 5 HI = CHI + 3 H 2 + 4 1 

I I 

CH 2 .OH CH 3 

Glycerol lsopropyl iodide 

CH 2 (OH).CH(OH).CH(OH).CH 2 (OH) + 7HI 

Erythrite 

= CH 3 .CH 2 ,CHI.CH 3 + 4 H 2 + 6I 

«-Sec. Butyl iodide 

CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CH 2 (OH)+nHI 

Mannite 

= CH 3 .CHI.CH 2 .CH 2 .CH 2 .CH 3 + 6H 2 0-{- iol 

«-Sec. Hexyl iodide 

With derivatives of alcohols, e.g. alcohol-acids (hydroxy acids) the 

first reaction takes place : 

CH 2 . OH . CH 2 . COOH + HI = CH 2 I . CH 2 . COOH + H 2 

j3-Hydroxyproprionic acid j3-lodoproprionic acid 

CH 2 (OH) . CH(OH) . COOH + 2 HC1 = CH 2 C1 . CHC1 . COOH + 2 H 2 

Glyceric acid a-/3-Dichlorproprionic acid 

2. The second reaction takes place much more energetically, espe- 
cially when a phosphorus halide which has been previously made is 
used. This is not always necessary, at least in introducing bromine 
and iodine; in many cases it is better to generate the phosphorus halides 
in the course of the reaction, by adding to the mixture of alcohol and 
red phosphorus either bromine from a dropping funnel, or as above, 
finely pulverised iodine. This reaction, as well as the first, is applicable 
to poly-acid alcohols and substituted alcohols, e.g. : 
(a) CH 2 (OH) . CH 2 (OH) + 2 PC1 5 = CH 2 C1 . CH 2 C1 + 2 POCl 3 + 2 HC1 

Ethylene glycol Ethylene chloride 

(d) CH 2 (OH) . CHC1 . CH 2 C1 + PC1 5 

Dichlorhydrine 

= CH 2 C1 . CHC1 . CH 2 C1 + POCl 3 + HC1 

Trichlorhydrine 

This example illustrates the more energetic action of the phosphorus 
halide as compared with the corresponding hydrogen halide ; it is im- 
possible to replace the third hydroxy 1 group of glycerol with chlorine 
by the use of hydrochloric acid. 

(0 CHo . CH (OH) . COOH + PCI. = CH 3 . CHC1 . COOH + P0C1 3 + HC1 

(I) (I) 

a-Hydroxyproprionic acid a-Chlorproprionic acid 

In cases of this kind a complication arises, due to the fact that the 
phosphorus halide also acts upon the hydroxyl of the carboxyl group, 
replacing it with the halogen, giving rise to an acid-chloride : 



ALIPHATIC SERIES 117 

CH 3 . CHC1 . CO . OH + PC1 5 = CH 3 . CHC1 . CO . CI + POCP + HC1 

The acid may be regenerated by treating the acid-chloride with water : 

CH 3 . CHC1 . CO . CI + H 2 = CH 3 . CHC1 . CO . OH + HC1 

The action of phosphorus iodide on poly-acid alcohols is similar to the 
action of hydriodic acid referred to under Reaction 1 . 

The more energetic action of the phosphorus halides may also be 
perceived in the fact that phenol hydroxy] groups can be replaced by a 
halogen, by the use of the phosphorus compounds, which, as mentioned 
above, is impossible with the halogen hydracids, e.g. : 



C r H 5 .OH -f-PCL 

Phenol (Br) 


= C 6 H 


5 .C1 + P0C1 3 + HC1 

(Br) 


/N0 2 
Ken +P ° 5 


= C 6 H. 


/NO., 
.< " + POCI, + HC1 
\C1 


/OH 
QH./ + PCI- 
\(N0 2 ), 

Picric acid 


= C 6 H 


/CI 
9 < + POCI3 + HC1 
XN0 2 ) 3 

Picryl chloride 



But the quantities obtained are much less satisfactory, the reason being 
that the phosphorus oxychloride attacks the unacted-upon phenol, form- 
ing phosphoric acid esters, e.g.: 

POCI3 + 3 C G H 5 . OH = PO . (OC f H 5 ) 3 + 3 HC1 

In this way a large portion of the phenol is withdrawn from the main 
reaction. 

The monohalogen alkyls C ?l H(2n+i) Cl(Br, I) are in most cases colour- 
less liquids, the exceptions being methyl and ethyl chlorides and methyl 
bromide, which, are gaseous at the ordinary temperature, and the mem- 
bers of the series having high molecular weights, like cetyl iodide, 
C lfi H 33 I, which are semi-solid, salve-like substances. The iodides are 
only colourless when freshly prepared ; on long standing, especially 
under the influence of light, a slight decomposition, resulting in the 
separation of iodine, takes place, imparting to them a faint pink colour 
at first, which becomes brownish red after a long time. This decom- 
position can be prevented if some finely divided, so-called molecular 
silver is added to the liquid. A coloured iodide can be made colourless 
by shaking it with some caustic soda solution. The halogen alkyls 
mix readily with organic solvents, as alcohol, ether, carbon disulphide, 



Il8 SPECIAL PART 

benzene, etc, but not with water. The chlorides are lighter, the bro- 
mides and iodides heavier than water; the latter have the highest 
specific gravities. This property decreases in all three classes with the 
decrease in halogen percentage from the lower up to the higher mem- 
bers of the series ; i.e. the higher molecular weight compounds have a 
smaller specific gravity than the lower members. The chlorides have 
the lowest boiling-points ; the corresponding bromides boil about 25 , 
and the iodides 50 higher. 

The ease with which the monohalogen alkyls react with other com- 
pounds gives them great importance ; they are used primarily as a means 
of introducing alkyl groups into other molecules, i.e. by replacing an 
hydrogen atom with an alkyl group. If it is desired, e.g., to replace in 
an alcohol, mercaptan, phenol, or acid the hydrogen of the (OH)-, 
(SH)-, or (COOH)-group by an alkyl radical, i.e. to prepare an ether 
of these substances, the corresponding sodium compound, or in case of 
acids, better the silver salt, is treated with the halogen alkyl, e.g. : 

C 2 H 5 . ONa + IC 2 H 5 = C 2 H 5 . . C 2 H 5 + Nal 

Sodium alcoholate Ethyl ether 

C 2 H 5 . SNa + IC 2 H 5 = C 2 H 5 . S . C 2 H 5 + Nal 

Sodium ethyl mercaptide Ethyl sulphide 

C 6 H S . ONa + ICH3 = C,H 5 . . CH 3 + Nal 

Sodium phenolate Phenyl methyl ether 

= Anisol 

CH 3 . COOAg + IC 2 H 5 = CH 3 . COO . C 2 H 5 + Agl 

Silver acetate Ethyl acetate 

The alkyl groups may be introduced into the ammonia molecule and 
into organic amine molecules by means of the halogen alkyls ; e.g. : 

NH 3 + ICH3 = NH 2 .CH 3 + HI 

Methyl amine 

Di- and tri-methyl amine are also formed at the same time. 
C 6 H 5 . NH 2 + 2 CH 3 C1 = C H 5 . N(CH 3 ) 2 + 2 HC1. 

Aniline Dimethyl aniline 

Hydrogen atoms in combination with carbon may also be replaced by 
alkyl radicals, by means of the halogen alkyls. Since under these con- 
ditions another radical is introduced into the molecule, it presents a 
method of preparing the higher members of a series from the lower, 
simpler ones. Various examples of this will be taken up later in labor- 



ALIPHATIC SERIES 119 

atory practice. Here it will be sufficient to refer to several equations 
showing this kind of reaction. 

CH 3 . CO . CHNa . COOC 2 H 5 + ICH 3 = CH 3 . CO . CH - COOC 2 H 5 + Nal 

Sodium acetacetic ester 

CH 3 

Methylacetacetic ester 

COOC 2 H, COOC 2 H, 

I I 

CHNa + IC 9 H 5 = CH - C 2 H 3 + Nal 

I " I 

COOC 2 H 5 COOC 2 H 5 

Sodium malonic ester Ethyl malonic ester 

C 6 H 6 + C1C 2 H 5 = C 6 H 5 . C 2 H 5 + HC1 

Benzene Ethyl benzene 

(In presence of A1C 3 ) 

Fittig's Synthesis, to be taken up later, is a case of this kind, by 
which a halogen atom is replaced by an alkyl group ; e.g. : 

C 6 H s Br + BrC 2 H 5 + 2 Na = C 6 H 5 .C 2 H 5 + 2 NaBr 

Brom benzene Ethyl benzene 

Further, the halogen alkyls serve for the preparation of the unsatu- 
rated hydrocarbons of the ethylene series. 

CH 3 . CHI . CH 3 = CH 3 . CH = CH 2 + HI 

Isopropyl iodide Propylene 

In many cases the alcohols may also be prepared from the halogen 
alkyls ; e.g. : 

CH3.CHI.CH3 + HOH = CHg.CH(OH) .CH 3 + HI 

Isopropyl alcohol 

This reaction is obviously only of importance when the halogen alkyl 
is not obtained from the corresponding alcohol, as is the case in the 
example given. As above mentioned, the isopropyl iodide is most 
simply obtained from glycerol and hydriodic acid, so that by this 
reaction the glycerol can be converted into the isopropyl alcohol 
(compare Reaction 13). Halogen alkyls also unite directly with other 
compounds, like sulphides and tertiary animes : 

/C 2 H 5 

/ r u 

C 2 H 5 . S . C 2 H 5 + IC 2 H 5 = S \^p u 
\l 2 

Ethyl sulphide Triethylsulphine iodide 



120 SPECIAL PART 

N(CH 8 ) 8 + CH 3 C1 = N(CH 3 ) 4 C1 

Trimethyl amine Tetramethyl ammonium chloride 

C 5 H 5 N + ICH 3 = C 5 H 5 N.ICH 3 

Pyridine Methylpyridine iodide 

With these examples the list of the many-sided reactions of the hal- 
ogen alkyls is not exhausted ; 'they are also used for the preparation 
of the metallic alkyls, e.g., zinc alkyls ; for the preparation of the 
phosphines, and for many other compounds. Finally, attention is 
called to the characteristic difference between the organic and inorganic 
halides. While, e.g., potassium chloride, bromide, or iodide in solu- 
tion act instantly with a silver nitrate solution to form a quantitative 
precipitate of silver chloride, bromide, or iodide respectively, silver 
nitrate in a water solution does not act on most organic halides, so 
that this reagent does not serve in the usual way to show the presence 
of a halogen. 

Experiment : Treat a solution of silver nitrate with a few 
drops of ethyl bromide. Not the least trace of silver bromide 
is formed. 1 

It has been customary to explain this by saying that the affinity 
between the halogen atom and carbon is greater than that between the 
halogen and the metallic atom. According to our later views the differ- 
ence between the two classes of compounds is explained thus : The 
metallic halides belong to the class of so-called electrolytes, i.e. sub- 
stances which are dissociated in water solution, e.g. the molecule KC1 

is dissociated into its ions, K and CI. The organic halides are non- 

+ - 

electrolytes, i.e. the solutions of these contain the undissociated mole- 
cules. According to this conception, the potassium chloride reacts 
with silver nitrate, because no further separation of the potassium from 
the chlorine (other than that effected by solution) is necessary, while in 
case of the brom alkyls, the brom-carbon union must first be severed. 
Only halogen ions react, at once, quantitatively with the silver ions of 
silver nitrate. 



1 A noteworthy exception is ethyl iodide, which when shaken with a water 
solution of silver nitrate, gives an abundant precipitate of silver iodide. Methyl 
iodide does not react with silver nitrate. 



ALIPHATIC SERIES 



121 



2. REACTION 



PREPARATION OF AN ACID-CHLORIDE FROM THE 
ACID 



Example : Acetyl Chloride from Acetic Acid l 

To ioo grammes of glacial acetic acid contained in a fraction- 
ating flask connected with a condenser (coil condenser), 80 
grammes of phosphorus trichloride are added through a dropping 
funnel, the flask being cooled by water. The bulb is then im- 




FlG. 64. 

mersed in a porcelain dish filled with water at a temperature of 
40-5 o°, and the heating continued until the active evolution of 
hydrochloric acid gas slackens, and the liquid which was homo- 
geneous before heating has separated into two layers. To sepa- 
rate the acetyl chloride which forms the upper, lighter layer, from 
the heavier layer of phosphorous acid, the mixture is heated on a 
rapidly boiling water-bath until nothing more passes over. Since 
acetyl chloride is very easily decomposed by moisture, the distillate 
1 A. 87, 63. 



122 SPECIAL PART 

must not be collected in an open receiver, but the condenser-tube 
must be tightly connected with a tubulated flask (suction flask), 
protected from the air by a calcium chloride tube, as represented 
in Fig. 64. For complete purification, the distillate is distilled in 
a similar apparatus, except that the dropping funnel is replaced by 
a thermometer. The apparatus represented in Fig. 17, page 21, 
may be used for the redistillation. The portion distilling from 
5 0-5 6° is collected in a separate vessel. Boiling-point of pure 
acetyl chloride, 51 . Yield, 80-90 grammes. 

In order to replace the hydroxyl of a carboxyl group (CO . OH) by 
chlorine, a reaction, similar to the one employed above for the substi- 
tution of an alcoholic hydroxyl group by a halogen, may be used. If, 
e.g., a mixture of an acid and phosphoric anhydride is treated with 
gaseous hydrochloric acid (heating if necessary), there is formed an 
acid-chloride, the reaction being analogous to that by which ethyl 
bromide was prepared. 

X.CO.OH + HCl = X.CO.Cl + H 2 

This reaction is without practical importance, since the reactions in- 
volved in the methods described under (2), page 116, take place much 
more smoothly and easily, and, therefore, are exclusively used. The 
above reaction is mentioned here only because it throws some light on 
one of the methods used in esterification, which will be briefly described 
below under the characteristics of the acid-chlorides. In practice, the 
acid-chlorides are almost always prepared by the action of phosphorus 
tri- or penta-chloride on the acid directly, or in many cases, on the 
sodium or potassium salt. Phosphorus oxychloride is employed in 
rare cases. The selection of the chloride of phosphorus depends upon 

(1) the ease with which the acid under examination reacts," and 

(2) upon the boiling-point of the acid-chloride. If, as in the case of 
acetic acid and its homologues, the trichloride of phosphorus reacts 
easily with the formation of the acid-chloride, this is selected in prefer- 
ence to the more energetic pentachloride. The reaction probably takes 
place in accordance with the following equation : 

3 CH 3 . CO . OH + 2 PC1 3 = 3 CH 3 . CO . CI + P 2 O s + 3 HO 
In cases in which the boiling-point of the acid-chloride desired does 
not lie far from that of phosphorus oxychloride (no ), thus rendering 
a fractional distillation for the separation of the products difficult, the 
trichloride is always used. If an acid does not react too energetically, 



ALIPHATIC SERIES 1 23 

as is the case with the higher members of the acetic acid series with 
the pentachloride, this is used. With the aromatic acids, the latter is 
used exclusively, since the trichloride and oxychloride react with great 

difficulty : 

C 7 H 15 . CO . OH + PC1 5 == C 7 H 15 . CO . CI + POCl 3 + HC1 

Caprylic acid 

C 6 H 5 . CO . OH + PC1 3 = C 6 H S . CO . CI + POCl 3 + HC1 

Benzoic acid Benzoyl chloride 

Attention is called to the fact that for one molecule of phosphorus 
pentachloride, but one molecule of the acid-chloride is obtained. 

The phosphorus oxychloride is used generally only when dealing 
with the salts of carbonic acids, upon which it acts as indicated by the 
equation : 

2 CH 3 . CO . ONa + POCI3 = 2 CH 3 . CO . CI + NaP0 3 + NaCl 

This reaction may be used with advantage in order to utilise more 
of chlorine of the phosphorus pentachloride than is the case when the 
latter acts upon the free acids. If the pentachloride is allowed to act 
on a sodium salt, as above, there is formed, for an instant, phosphorus 
oxychloride, and while this no longer acts upon the free acid, it can 
convert two other molecules of the salt into the chloride : 

3 CH 3 . CO . ONa + PC1 5 = 3 CH 3 . CO . CI + NaP0 3 + 2 NaCl 

In this way, with the use of one molecule of phosphorus pentachloride, 
three molecules of the acid-chloride are obtained. 

The lower members of the series of acid-chlosides are colourless 
liquids; the higher, colourless crystalline substances. They boil, gen- 
erally, at ordinary pressure without decomposition, but the higher 
members are more conveniently distilled in a vacuum. The boiling- 
points of the acid-chlorides are lower than those of the acids ; the 
replacement of hydroxyl by chlorine usually causes a lowering of the 
boiling-point. 



CHo.CO.Cl Boiling-point 51 


C 6 H 5 . CO . CI Boiling-point 199 


CH3.CO.OH " 118 


C 6 H 5 .CO.OH " 250 



The acid-chlorides possess pungent odours. They fume in the air, since 
they unite with the moisture and decompose, thus forming the corre- 
sponding acid and hydrochloric acid. They are heavier than water, 
and do not mix with it, but are easily soluble in indifferent organic 
solvents like ether, carbon disulphide, benzene. 



124 SPECIAL PART 

To separate the chlorides from the by-products formed by the phos- 
phorus chloride, one can proceed as in the case of acetyl chloride, by 
distilling off the volatile chloride from the non-volatile phosphorus acid, 
either on a water-bath or over a free flame. In order to separate a 
chloride, in case it distils without decomposition, from the volatile phos- 
phorus oxychloride formed when phosphorus pentachloride is used, a 
fractional distillation is made. In other cases, the mixture is heated 
in a vacuum apparatus on an actively boiling water-bath, upon which 
the phosphorus oxychloride passes over. The non-volatile residue 
can be used, in many cases, without further purification ; it may be 
obtained perfectly pure by distilling it in a vacuum. 

* Chemical Reactions. — The acid-chlorides are decomposed by water 
with the formation of the corresponding acid and hydrochloric acid. 

CH 3 . CO . CI + H 2 = CH 3 . CO . OH + HC1. 

This decomposition takes place often with extreme ease ; the chlorine 
atom is united to the acid radical much less firmly than it is in the case 
of an alkyl radical. While it is generally necessary, in order to convert 
a halogen alkyl into an alcohol, to boil it a long time with water, often 
with the addition of sodium hydroxide, or potassium hydroxide, a car- 
bonate or acetate, the analogous transformation of an acid-chloride 
takes place with far greater ease. With the lower members, e.g., acetyl 
chloride, the reaction begins almost instantly at the ordinary tempera- 
ture, and continues with violent energy ; but it is necessary to heat the 
higher members to induce the transformation, e.g., benzoyl chloride, 
which will be prepared later. 

Experiment: To 5 c.c. of water in a test-tube is gradually 
added \ c.c. of acetyl chloride. If the water is very cold, the 
oily drops, sinking to the bottom, do not mix with it, and may be 
observed for a short time. On shaking the tube, an energetic 
reaction sets in with evolution of heat, and the chloride passes 
into solution, which happens immediately if the water is not 
cold. 

The acid-chlorides react with alcohols and phenols to form esters : 

CH 3 . CO . CI + C 2 H 5 OH = CH 3 . CO . OC 2 H 5 + HC1 

Ethyl acetate 

CH 3 . CO . CI + C 6 H 5 . OH = CH 3 . CO . OC 6 H s + HC1 

Phenol Phenyl acetate 



ALIPHATIC SERIES 1 25 

Experiment : To 1 c.c. of alcohol in a test-tube, cooled with 
water, add an equal volume of acetyl chloride, drop by drop ; 
this mixture is then treated with an equal volume of water, the 
tube being cooled as before ; the liquid is then carefully made 
weakly alkaline with sodium hydroxide. If the pleasant-smelling 
ethyl acetate does not separate out on the water solution in a 
mobile layer, finely pulverised salt is added until no more will 
dissolve. This will cause the ethyl acetate to separate out. 

For the preparation of an ester, the previously prepared chloride is 
rarely used ; the method of procedure being to pass gaseous hydrochloric 
acid into a mixture of the corresponding acid and alcohol to saturation. 

There is probably formed, from the carbonic and hydrochloric acids, 
an intermediate acid-chloride which, as just described,**reacts with the 
alcohol. The acid-chlorides are also used to determine whether a sub- 
stance under examination contains an alcoholic or a phenol hydroxyl 
group or not. If the compound reacts readily with an acid-chloride, it 
contains either alcoholic or phenol hydroxyl, since compounds contain- 
ing oxygen in some other form of combination, e.g., as in ethers, do not 
react with acid-chlorides. 

The addition of anhydrous sodium acetate often materially assists the 
reaction. 

Finally, the action of the acid-chlorides upon alcohols and phenols 
is made use of to separate the latter from solution, or in order to detect 
them. However, benzoyl chloride is most generally used for this pur- 
pose, concerning the importance of which more will be said later. 

Acid-chlorides act upon the salts of carbonic acids, forming anhy- 
drides : 

CH 3 . CO . CI + CH 3 . CO . ONa = CH 3 . CO . O . CO . CH 3 + NaCl 

Acetic anhydride 

The next preparation will deal with this reaction. The acid-chlorides 
react with ammonia as well as with primary and secondary organic 
bases with great ease : 

CH, . CO . CI + NH 3 = CH 3 . CO . NH 2 + HC1, 

Acetamide 

CHo.CO.Cl + C 6 H S . NH 2 = C 6 H 5 .NH . CO . CH 3 + HC1 

Aniline Acetanilide 

Experiment : To 1 c.c. of aniline, acetyl chloride is added in 
drops ; an energetic reaction takes place with a hissing sound, 



126 SPECIAL PART 

which ceases when about the same volume of the chloride is added. 
The mixture is cooled with water, and five times its volume of 
water is added, upon which an abundant precipitate of acetanilide 
separates out, the quantity of which is increased by rubbing the 
walls of the test-tube with a glass rod. The precipitate is filtered 
off, and recrystallised from hot water. Melting-point, 115 . 

This reaction is also used to characterise organic bases by converting 
them into their best crystallised acid derivatives, and in order to detect 
small quantities, especially of liquid bases, by a melting-point deter- 
mination. Since the tertiary bases do not react with acid-chlorides, 
because they no longer contain any ammonia hydrogen, this reaction 
may be employed to decide whether a given base is, on the one hand, 
primary or secondary, or, on the other, tertiary. 

The fact that hydrogen in combination with carbon can be replaced 
by an acid radical by the use of an acid-chloride is of special importance. 
In this connection, the Friedel-Crafts ketone synthesis is particularly 
mentioned. This will be taken up later, in practice. The reaction is 
indicated by the following equation : 

C 6 H fi + CH, . CO . CI = C 6 H 5 . CO . CH 3 + HC1 

Benzene Acetophenone 

(in presence of AIC1 3 ) 

The acid-chlorides are also of service for the synthesis of tertiary 
alcohols (Butlerow's Synthesis), as well as for that of ketones. The 
final reactions will only be indicated here ; in regard to the details, 
reference must be made to larger works. 



CH3.CO.Cl + Zn< = CH 3 .C^CHn + ZnO 

\CH 3 \ C 1 

Zinc methyl 

/CH 3 /th 

CH 3 .C^CH 3 + H 2 = C<^ + Ha 

U X OH 

Trimethyl carbinol 



2 CH 3 . CO . CI + Zn< = 2 CHo . CO . CH, + ZnCl, 

\CH 3 

Acetone 



ALIPHATIC SERIES 1 27 



3. REACTION: PREPARATION OF AN ANHYDRIDE FROM THE ACID- 
CHLORIDE AND THE SODIUM SALT OF THE ACID 

Example : Acetic Anhydride from Acetyl Chloride 
and Sodium Acetate 1 

For the preparation of acetic anhydride an apparatus similar 
to that used in the preparation of acetyl chloride is employed, 
except that the fractionating flask is replaced by a tubulated retort 
(Fig. 65, page 128). 2 

To 70 grammes of finely pulverised, anhydrous sodium acetate 
(for the preparation of this, see below) contained in the retort, 
50 grammes of acetyl chloride are added drop by drop from a 
separating funnel. As soon as the first half of the chloride is 
added, the reaction is interrupted for a short time, in order that 
the pasty mass may be stirred up with a glass rod. The second 
half is then allowed to run in. If in consequence of a too rapid 
addition of acetyl chloride some of it should distil over into the 
receiver undecomposed, this is poured back into the funnel and 
again allowed to act on the sodium acetate. The separating 
funnel is then removed, the tubulure closed with a cork, and the 
anhydride distilled off from the salt residue by means of a luminous 
flame which is kept in constant motion. The distillate is finally 
purified by distilling in an apparatus similar to the one used in the 
rectification of the acetyl chloride (see also Fig. 17) with the 
addition of 3 grammes of finely pulverised anhydrous sodium 
acetate, which serves to convert the last portions of acetyl chloride 
into the anhydride. Boiling-point of acetic anhydride, 138 . 
Yield, about 50 grammes. 

Preparation of Anhydrous Sodium Acetate : Crystallised sodium 
acetate contains three molecules of water of crystallisation. In 
order to dehydrate it is placed in a shallow iron or nickel dish and 
heated over a free flame (120 grammes for this experiment). The 
salt first melts in the water of crystallisation, on further heating 
steam is copiously evolved, and the mass solidifies as soon as 

1 A. 87, 149. 

2 An upright coil condenser may be used, in which case an adapter is unnecessary. 



128 SPECIAL PART 

the main portion of the water has been driven off, provided the 
flame is not too large. In order, to remove the last portions of the 
water, the mass is now heated with a large flame, the burner being 
constantly moved, until the solidified mass melts for the second time. 
Care must be taken not to overheat; in case this should happen, 



FIG. 65. 

the fact will be recognised by the evolution of combustible gases and 
the charring of the substance. After cooling, the salt is removed 
from the dish with a knife. If commercial anhydrous sodium 
acetate is at hand, it is recommended that this also be melted once, 
since when it is kept for a long time it always takes up water. 

The reaction of acetyl chloride with sodium acetate takes place in 
accordance with the following equation : 

CH 3 CO\ 
CH 3 . CO . CI + CHo . CO . ONa = >0 + NaCl 

CH3CO/ 

This reaction is capable of general application, and the anhydride of 
the acid may be made by treating its chloride with the corresponding 
sodium salt. The so-called mixed anhydrides, containing two different 



ALIPHATIC SERIES 1 29 

acid radicals, can also be prepared by this reaction, by using the chloride 
and sodium salt of two different acids : 

CH 3 .C(X 
CH,.CO.Cl + CH,.CH 2 .CO.ONa= >0 +NaCl 

CH 3 .CH 2 .CO/ 

Since, as stated, an acid-chloride may be obtained from an alkali salt of 
the acid and phosphorus oxychloride, it is not necessary for the prepa- 
ration of an anhydride to first isolate the chloride ; it is better to allow 
the same to act directly on an excess of the salt, so that from the oxy- 
chloride and salt an anhydride is directly obtained : 

2 CH 3 . CO . ONa + POCI3 = 2 CH 3 . CO . CI + P0 3 Na + NaCl 

CH 3 .CO\ 
2CH,.CO.ONa + 2CH 3 .CO.Cl = 2 >0 + 2 NaCl 

CPL.CO/ 



4 CH 3 . CO . ONa + POCL = 2 >0 + P0 3 Na + 3 NaCl 

CH 3 .CO/ 

The lower members of the acid-anhydride series are colourless liquids ; 
the higher members, crystallisable solids. They possess a sharp odour, 
are insoluble in water, but soluble in indifferent organic solvents. Their 
specific gravities are greater than that of water. The boiling-points 
are higher than those of the corresponding acids : 

Acetic acid, n 8°, 
Acetic anhydride, 138 . 

The lower members can be distilled without decomposition at ordinary 
pressure ; but the higher members must be distilled in a vacuum. 

The chemical conduct of anhydrides toward water, alcohols, and 
phenols, as well as bases, is wholly analogous to that of the chlorides ; 
but the anhydrides react with more difficulty than the chlorides. Thus 
with water, the anhydrides yield the corresponding acids : 

CH 3 .CO\ 

>0 + H.,0 = 2CH 3 .CO.OH 
CHo.CO/ 

Experiment : 5 c.c. of water are treated with -J c.c. of acetic 
anhydride. The latter sinks to the bottom and does not dissolve 
even on long shaking. It will be recalled that the corresponding 
chloride reacts instantly with water very energetically. If the 
mixture be warmed, solution takes place. 



130 SPECIAL PART 

In the presence of alkalies, solution takes place much more readily 
with the formation of the alkali salts : 

CH 3 .CCK 

>0 + 2NaOH = 2CHo.C0.0Na + H 2 
CH3.CO/ 

Experiment : Mix 5 c.c. of water with \ c.c. of acetic anhy- 
dride, and add a little caustic soda solution. On shaking, without 
warming, solution takes place. 

Anhydrides of high molecular weight react with water with still 
greater difficulty, and require a longer heating to convert them into the 
corresponding acid. 

With alcohols and phenols, the anhydrides form acid-esters on heat- 
ing, while the acid-chlorides react at the ordinary temperature : 



CH..CO 



> 



C 2 H 5 . OH = CH 3 . CO . OC 2 H 5 + CH 3 . CO . OH 



CHo.CO 

C G H 5 .OH = CH v CO.OC 6 H, + CH..CO.OH 

CH 3 . CO/ Phenyl acetate 



It is to be noted that one of the two acid radicals in the anhydride is 
not available for the purpose of introducing the acetyl group into other 
compounds, — acetylating, — since it passes over into the acid. 

Experiment : 2 c.c. of alcohol are added to 1 c.c. of acetic anhy- 
dride in a test-tube, and heated gently for several minutes. It is 
then treated with water and carefully made slightly alkaline. The 
acetic ester can be recognised by its characteristic pleasant odour. 
If it does not separate from the liquid, it may be treated with 
common salt, as in the experiment on page 125. 

With ammonia and primary or secondary organic bases, the anhy- 
drides react like the chlorides : 

CHg.ax 

NH 3 + >0 ..= CH 3 .CO.NH 2 + CH 3 .CO.OH 

CH 3 .CO/ 

CH 3 .CO 
CH 3 .CO 



CHg.CtK 
C 6 H 5 .NH 2 + >0 = C 6 H 5 .NH.CO.CHo + CH 3 .CO.OH 

CHo.CO/ 



ALIPHATIC SERIES 131 

Experiment : Add 1 c.c. of aniline to 1 c.c. of acetic anhydride, 
heat to incipient ebullition, and then, after cooling, add twice the 
volume of water. The crystals of acetanilide separate out easily 
if the walls of the vessel be rubbed with a glass rod ; these are 
filtered off, and may be recrystallised from a little hot water. 

The acid-anhydrides can, therefore, be used, like the chlorides, for 
the recognition, separation, characterisation, and detection of alcohols, 
phenols, and amines. 

In order to complete the enumeration of the reactions of the acid- 
anhydrides, it may be mentioned briefly that they yield alcohols, and 
the intermediate aldehydes when treated with sodium amalgam : 



>0 + H 2 = CH 3 . CHO + CH 3 . CO . OH 

CHo.CO/ Aldehyde 

CH 3 . CHO + H, = CH 3 . CH 2 . OH 

It is, therefore, possible to pass from the anhydride of an acid to its 
aldehyde or alcohol. 

4. REACTION: PREPARATION OF AN ACID-AMIDE FROM THE 
AMMONIUM SALT OF THE ACID 

Example : Acetamide from Ammonium Acetate 1 

To 75 grammes of glacial acetic acid heated to 40-50 in a 
porcelain dish on a water-bath, finely pulverised ammonium car- 
bonate is added (100 grammes will be necessary) until a test- 
portion diluted in a watch-glass with water just shows an alkaline 
reaction. The viscous mass is warmed on an actively boiling 
water-bath to 80-90 , until a few drops of it diluted with water 
just show an acid reaction ; it is then poured (without the use of 
a funnel-tube) directly into two wide bomb-tubes of hard glass, 
which have been previously warmed in a flame. A single Volhard 
tube (see page 63) is much more convenient. After the por- 
tions of substance adhering to the upper end of the tube have 
been removed by melting down carefully with a flame, the last 
traces are removed with filter-paper, the tube sealed and heated 

1 B. 15, 979. 



132 SPECIAL PART 

for five hours in a bomb-furnace at 220-230 . The liquid re- 
action product is fractionated under the hood in a distilling-flask 
provided with a condenser. There is first obtained a fraction 
boiling between 100-130 , consisting essentially of acetic acid and 
water. The temperature then rises rapidly to 180 (an extension 
tube is substituted for the condenser, see page 22), at which 
point the acetamide begins to distil. The fraction passing over 
between 180-230 is collected in a beaker, cooled by ice water 
at the end of the distillation, and the walls are rubbed with a 
sharp- edged glass rod ; the crystals separating out are pressed on 
a drying plate to remove the liquid impurities. By another dis- 
tillation of the pressed-out crystals, the almost pure acetamide 
boiling at 223 passes over. Yield, about 40 grammes. The 
product thus obtained possesses an odour very characteristic of 
mouse excrement ; this is not the odour of pure acetamide, but 
of an impurity accompanying it. In order to remove the im- 
purity, a portion of the distilled amide is again pressed out on a 
drying plate, and then crystallised from ether. There are thus 
obtained colourless, odourless crystals, melting at 82 . 

The reaction involved in the preparation of an amide from the am- 
monium salt of the acid is capable of general application. The latter 
is subjected to dry distillation, or more conveniently, heated in a sealed 
tube at 220-230 for five hours : 

CH 3 . CO . ONH 4 = CH 3 . CO . NH 2 + H 2 
In order to purify the amide thus obtained, the reaction-mixture may be 
fractionated, as in the case of acetamide, or if the amide separates out 
in a solid condition, it may be purified by filtering off the impurities and 
crystallising. Substituted acid-amides, and especially easily substituted 
aromatic amides, e.g. acetanilide, can also be readily obtained by this 
method, by heating a mixture of the acid and amine a long time in an 
open vessel : 

CH 3 . COOH3N . C 6 H 5 = CH 3 . CO . NH . C 6 H 5 + H 2 

Aniline acetate Acetanilide 

The ammonium salts of di- and poly-basic acids react in a similar way, 

*&'- CO.ONH 4 CO.NH 9 

I =1 +2H 2 

CO.ONH 4 CO.NH 2 

Ammonium oxalate Oxamide 



ALIPHATIC SERIES I 33 

Concerning further methods of preparation, it may be stated that 
acid-chlorides or anhydrides when treated with ammonia, primary or 
secondary bases form acid-amides very easily : 

CH,.CO.Cl + NH 3 = CH 3 .C0.NH 2 + HC1 

\ 
>0 + NH 3 = CH,.CO.NH 2 + CH 3 .CO.OH 
CH 3 .CO/ 

The acid-amides may be furthermore obtained by two methods of 
general application: (i), by treating an ethereal salt with ammonia, 
and (2), by treating a nitrile with water: 

CH 3 . CO - OC 2 H 5 + NH 3 = CH 3 . CO . NH 2 + C 2 H 5 . OH 

Ethyl acetate 

CH 3 . CN + H 2 = CH 3 . CO . NH 2 

Acetonitrile 

The acid-amides are, with the exception of the lowest member, 
formamide, H . CO . NH 2 (a liquid), colourless, crystallisable compounds, 
the lower members being very easily soluble in water, e.g., acetamide ; 
the solubility decreases with the increase of molecular weight, until 
finally they become insoluble. The boiling-points of the amides are 
much higher than those of the acids : 



Acetic acid, Boiling-point, 118 
Acetamide, „ 223 



Proprionicacid, Boiling-point, 141 ° 
Proprionamide, „ 213 



While the entrance of an alkyl residue into the ammonia molecule 
does not change the basic character of the compound, as will be dis- 
cussed more fully under methylamine, the entrance of a negative acid 
radical enfeebles the basic properties of the ammonia residue, so that 
the acid-amides possess only a very slight basic character. It is true that 
a salt corresponding to ammonium chloride — CH 3 .CO.NH 2 .HCl — 
can be prepared from acetamide by the action of hydrochloric acid ; 
but this shows a strong acid reaction, is unstable, and decomposes 
easily into its components. If it is desired to assign to the acid-amides 
a definite character, they must be regarded as acids rather than bases. 
One of the amido-hydrogen atoms possesses acid properties in that it 
may be replaced by metals. The mercury salts of the acid-amides may 
be prepared with especial ease, by boiling the solution of the amide 
with mercuric oxide : 

HgO =(CH 3 .CO.NH) 2 Hg + H 2 



134 SPECIAL PART 

Experiment : Some acetamide is dissolved in water, treated 
with a little yellow mercuric oxide, and warmed. The latter goes 
into solution, and the salt of the formula given above is formed. 

The amido-hydrogen atoms can also be replaced by the negative 
chlorine and bromine atoms, as well as by the positive metallic atoms. 
These substitution compounds are obtained by treating the amide with 
chlorine or bromine, in the presence of an alkali : 

CH 3 . CO . NHC1 CH 3 . CO . NHBr CH 3 . CO . NBr 2 

Acetchloramide Acetbromamide Acetdibromamide 

The monohalogen substituted amides are of especial interest, since, on 
being warmed with alkalies, they yield primary alkylamines : 

CH 3 . CO . NHBr + H 2 = CH 3 . NH 2 + HBr + C0 2 

This important reaction will be taken up later, under the preparation 
of methyl amine from acetamide. 

In the acid-amides, the acid radical is not firmly united with the 
ammonia residue ; this is shown by the fact that they are saponified, 
i.e. decomposed into the acid and ammonia, on boiling with water, 
more rapidly by warming with alkalies : 

CH 3 . CO . NH 2 + H 2 = CH 3 . CO . OH + NH 3 

Experiment : Heat some acetamide in a test-tube with caustic 
soda solution. An intensely ammoniacal odour is given off, while 
the solution contains sodium acetate. 

If an acid-amide is treated with a dehydrating agent, e.g., phosphorus 
pentoxide, it is converted into a nitrile : 

CH 3 . CO . NH 2 = CH 3 . CN + H 2 

Acetonitrile 

The same result is obtained by treating it with phosphorus penta- 
chloride ; but in this case the intermediate products, the amide-chlorides 
or imide-chlorides are formed : 

CH 3 . CO . NH 2 + PCI. = CH 3 . CC1 2 . NH 2 + POCl 3 

Amide-chloride 

The very unstable amide-chloride then passes over, with the loss of one 
molecule of hydrochloric acid, into the more stable imide-chloride : 
CH 3 .CC1 2 .NH 2 = CH 3 .CC1=NH + HC1 

Imide-chloride 

And this finally into the nitrile, 

CH 3 . CC1 = NH = CH 3 . CN + HC1 



ALIPHATIC SERIES 135 

5. REACTION: PREPARATION OF AN ACID-NITRILE FROM AN 
ACID- AMIDE 

Example : Acetonitrile from Acetamide ! 

To 15 grammes of phosphoric anhydride, contained in a small, 
dry flask, 10 grammes of dry acetamide are added. After the two 
substances are shaken well together, the flask is connected with a 
short condenser, and then heated carefully, with a not too large 
luminous flame kept in constant motion. The reaction proceeds 
with much foaming. After the mixture has been heated a few 
minutes, the acetonitrile is then distilled over with a large luminous 
flame, kept in co7istant motion, into the receiver (test-tube). The 
distillate is treated with half its volume of water, and then solid 
potash is added until it is no longer dissolved by the lower layer 
of liquid. The upper layer is removed with a capillary pipette 
and distilled, a small amount of phosphoric anhydride being placed 
in the fractionating flask for the complete dehydration of the nitrile. 
Boiling-point, 82 . Yield, about 5 grammes. 

If an acid-amide is heated with a dehydrating agent (phosphorus 
pentoxide, pentasulphide, or pentachloride), it loses water, and passes 
over into the nitrile, e.g. : 

CH 3 .CO NH 2 = CH 3 .C=N + H 2 

Acetonitrile 

Since, as has just been done, the acid-amide may be made by dehy- 
drating the ammonium salt of an acid, thus, in a single operation the 
nitrile may be obtained directly from the ammonium salt, if it is treated 
with a powerful dehydrating agent, e.g. ammonium acetate heated with 
phosphoric anhydride : 

CH 3 . COONH 4 = CH 3 . CN + 2 H 2 

The acid-nitriles may also be obtained by heating alkyl iodides (or 
bromides, chlorides) with alcoholic potassium cyanide : 







CH 3 |I + 1 

CH.,Br 

1 
CH 2 Br 


<L\CN 

+ 2KCN 


= CH 3 
CH 2 

CH 9 

Eth; 


.CN + KI 

.CN 

+ 2KBr 
.CN 

ylene cyanide 


1A. 


64, 


33a. 





136 SPECIAL PART 

C 6 H 5 . CH 2 . CI + KCN = C 6 H 5 . CH 2 . CN + KC1 

Benzyl chloride Benzyl cyanide 

or by the dry distillation of alkyl alkali sulphates with potassium 
cyanide : 

/0\ C 2 U 5 cn| k 

S0 2\ + =C,H 5 .CN + K 2 S0 4 

X)K 

Ethyl potassium sulphate Proprionitrile 

These two reactions differ from those above in that the introduction of 
a new atom of carbon is brought about. The nitriles thus appear to be 
cyanides of the alkyls, and, therefore, may be equally well designated 
as cyanides, e.g. : 

CH 3 . CN = Acetonitrile = Methyl cyanide 
C 2 H 5 . CN = Proprionitrile = Ethyl cyanide 
etc. etc. etc. 

The lower members of the nitrile series are colourless liquids, the 
higher members, crystallisable solids ; the solubility in water decreases 
with the increase in molecular weights. If they are heated with water 
up to 180° under pressure, they take up one molecule of water and are 
converted into the acid-amides : 

CH 3 .CN + H 2 = CH 3 .CO.NH 2 

On heating with acids or alkalies, they take up two molecules of water, 
and pass over into the ammonium salt as an intermediate product : 

CH 3 . CN + 2 H 2 = CH 3 . COONH 4 

which immediately reacts with the alkali or acid, in accordance with 
the following equations : 

CH 3 .COONH 4 + KOH = CH 3 .COOK + NH 3 + H 2 
CH 3 .COONH 4 + HC1 = CH 3 .COOH + NH 4 C1 

This process is called "saponification. 1 ' 

If nascent hydrogen (e.g.. from zinc and sulphuric acid) be allowed 
to act on nitriles, primary amines are formed (Mendius' reaction) : 1 



Ethyl amine 



1 A. I2i, 129. 



ALIPHATIC SERIES 1 37 

Further, but of less importance, general reactions may be indicated 
by the following equations : 

CH 3 . CN + H 2 S = CH 3 . CS . NH 2 

Thioacetamide 

CH,.CO\ 
CH 3 . CN + CH.> . CO . OH = >NH = Diacetamide 

CH3.CO/ 
CHo.CO\ 
CH 3 . CN + >0 = N(CO . CHo) 3 = Triacetamide 

CH 3 .CO/ 

.N.OH 
CH 3 .CN + NH 2 .OH = CH 3 .Cf 

X NH 2 

Hydroxylamine Acetamide-oxime 



CH 3 .CN + HC1 =CH 3 .C 






Imide-chloride 



6. REACTION: PREPARATION OF AN ACID-ESTER FROM THE ACID 
AND ALCOHOL 

Example : Acetic Ester from Acetic Acid and Ethyl Alcohol x 

A -J-litre flask, containing a mixture of 50 c.c. of alcohol and 50 
c.c. of concentrated sulphuric acid, is closed by a two-hole cork ; 
through one hole passes a dropping funnel, through the other a 
glass delivery tube connected with a long condenser or coil con- 
denser. The mixture is heated in an oil-bath to 140 (thermome- 
ter in oil) ; when this temperature is reached, a mixture of 400 c.c. 
of alcohol and 400 c.c. of glacial acetic acid is gradually added 
through the funnel, at the same rate at which the ethyl acetate 
(acetic ester), formed in the reaction, distils over. In order to 
remove the acetic acid carried over, the distillate is treated in an 
open vessel with a dilute solution of sodium carbonate until the 
upper layer will not redden blue litmus paper. The layers are 
now separated with a dropping funnel ; the upper layer is filtered 
through a dry folded filter, and shaken up with a solution of 100 



1 Bl. 33, 350. 



138 SPECIAL PART 

grammes of calcium chloride in 100 grammes of water, in order 
to remove the alcohol. The two layers are again separated with 
the funnel, the upper one dried with granular calcium chloride 
and then distilled on the water-bath (see page 16). Boiling- 
point, 7 8°. Yield, about 80-90% of the theory. 

Acid-esters can be obtained directly by the action of acids on 
alcohols: 

I. CH 3 .CO.OH + C 2 H 5 .OH = CH 3 .CO.OC 2 H 5 + H 2 

A reaction of this kind never takes place to any degree in quantitative 
proportions, since, as soon as a certain quantity of the ester is formed, 
and the corresponding quantity of water, the latter saponifies the ester, 
in accordance with the following equation : 

II. CH 3 . CO . OC 2 H 3 + H 2 = CH 3 . CO . OH + C 2 H 5 . OH 

In such cases, a condition of equilibrium is reached, in which an equal 
number of molecules of the ester are formed, according to equation I., 
and decomposed, according to equation II., at the same time. There 
are several methods by the use of which this condition may be changed. 
The saponifying action of the water must be neutralised ; accordingly 
a dehydrating agent is added to the mixture, sulphuric acid being fre- 
quently used for this purpose in the preparation of acid-esters. In 
many cases, where the salts of organic acids are more readily obtained 
than the free acids, they may be used for the preparation of the esters 
by heating them directly with alcohol and sulphuric acid. Other meth- 
ods for the preparation of acid-esters have been referred to, and, in 
part, carried out practically on the small scale in the foregoing prepara- 
tions, so that at this point it is only necessary to recall the equations : 

(1) CH 3 .CO.OAg + IC 2 H 5 = CH 3 . CO . OC 2 H 5 + Agl 

(2) CH 3 . CO . CI -f C 2 H 5 . OH = CH 3 . CO . OC 2 H 5 + HC1 

It will be remembered that, in these reactions, the previously prepared 
chloride was not used, but that hydrochloric acid was conducted into 
a mixture of the acid and alcohol (see acetyl chloride), or the acid was 
heated with alcoholic hydrochloric acid (see B. 28, 3252). 

CH 3 . CO\ 
(3) /O + C 2 H 5 . OH = CH 3 . CO . OC 2 H 5 + CH 3 . CO . OH 

CH 3 .CO/ 



ALIPHATIC SERIES 139 

Concerning the purification of the acid-esters, it may be mentioned, 
that the crude reaction-product is shaken with a sodium carbonate 
solution until the ester no longer shows an acid reaction. The 
alcohol may be removed from esters difficultly soluble in water by 
repeatedly washing with water ; in case an ester is moderately soluble 
in water, as ethyl acetate, it is better to use a solution of calcium 
chloride. 

The lower members of the series of acid-esters are colourless liquids 
with pleasant, fruit-like odours ; the higher members, as well as those 
of the aromatic acids, are crystallisable compounds. The boiling-points 
of esters containing alkyl residues of small molecular weights (CH 3 , 
C 2 H-, C 3 H r ) are lower than those of the corresponding acids ; the 
entrance of more complex alkyl residues raises the boiling-points : 

CH 3 .CO.OCH, Boiling-point, 57 

CH 3 .CO.OC 2 H 5 " " 78 

CH3.CO.OH ' " " 118 

CH 3 .CO.OC 6 H 13 " " 1 69° 

Hexyl acetate 

As already mentioned, the esters are saponified by heating with water: 

CH 3 . CO . OC 2 H 5 + H,0 = CH 3 . CO . OH + C 2 H 5 . OH 

The saponification is effected more readily by heating with alkalies : 

CH 3 . CO . OC 2 H 5 + KOH = CH 3 . CO . OK + C 2 H 5 . OH 

Other methods of saponification will be further discussed when a 
practical example is taken up. The action of ammonia upon acid- 
esters, forming acid-amides, has already been referred to under acet- 
amide : 

CH 3 . CO . OC 2 H 5 + NH 3 = CH 3 . CO . NH 2 + C 2 H 5 . OH. 



7. REACTION: SUBSTITUTION OF HYDROGEN BY CHLORINE 

Example : Monochloracetic Acid from Acetic Acid and Chlorine 1 

A current of dry chlorine is passed into a mixture of 150 
grammes of glacial acetic acid and 1 2 grammes of red phosphorus, 
contained in a flask provided with a delivery tube and an inverted 



1 R. 23, 222 ; A. 102, 1. 



140 SPECIAL PART 

condenser; the flask is heated on a rapidly boiling water-bath, 
and must be placed in such a position as to receive as much light 
as possible. The best result is obtained by performing the reac- 
tion in the direct sunlight, since the success of the chlorination 
depends essentially on the action of the sun's rays. The reaction 
is ended when a small test- portion cooled with ice-water solidifies 
on rubbing the walls of the vessel (test-tube) with a glass rod. 
In summer the chlorination may require a single day, while dur- 
ing the cloudy days of winter, two days may be necessary. For 
the separation of the monochloracetic acid the reaction-product is 
fractionated from a distilling flask connected with a long air con- 
denser. The fraction passing over from 150-200 is collected in 
a separate beaker ; this is cooled in ice-water and the walls rubbed 
with a glass rod. The portion solidifying, consisting of pure mono- 
chloracetic acid is rapidly filtered with suction, the loose crystals 
being pressed together with a spatula or mortar-pestle. The suc- 
tion must not be continued too long, because the monochloracetic 
acid gradually becomes liquid in warm air. The filtrate is again 
distilled, and the portion passing over between 170-200 is col- 
lected in a separate vessel. This is treated as before (cooling 
and filtering), and there is obtained a second portion of mono- 
chloracetic acid ; this is united with the main quantity, which is 
again distilled. The product thus obtained is perfectly pure. 
Boiling-point, 186 . Yield varying, 80-125 grammes. 

Since monochloracetic acid, especially when warm, attacks the 
skin with great violence, care must be taken in handling it. 

Chlorine or bromine substitution products of aliphatic carbonic acids 
can be obtained by the direct action of the halogen on the acids : 

CH3.CO.OH + Cl 2 = CHoCl.CO.OH + HC1 
(Br,) (Br) (HBr) 

If the reaction is allowed to continue for a long time, other substitution 
products can also be obtained. But the action of chlorine or bromine 
on acids is very sluggish. It may be essentially facilitated by certain 
conditions. If, e.g., the operation is conducted in direct sunlight, the 
reaction proceeds much more rapidly than in a dark place. The reac- 
tion is assisted more effectively by adding a so-called " carrier." Iodine 



ALIPHATIC SERIES 141 

may be used as such for the introduction of chlorine or bromine. When 
added in small quantities to the substance to be substituted, it causes 
the substitution to take place more rapidly and completely. The con- 
tinuous action of this carrier depends upon the following facts : In 
the first phase of the reaction, chlorine iodide is formed : 

(1) CI + I = IC1 

This acts, then, as a chlorinating agent in the second phase, according 
to the following reaction : 

(2) CH 3 . CO . OH + IC1 = CHoCl . CO . OH + HI 

The chlorine acts upon the hydriodic acid as follows : 

(3) HI + Cl 2 = IC1 + HC1 

The molecule of chlorine iodide is thus formed anew (equation 1) 
and can chlorinate another molecule of acetic acid, and so on. The 
action of the iodine in the last case depends upon the fact that the 
molecule of chlorine iodide (1C1) is more easily decomposed into its 
atoms than the molecule of chlorine (Cl 2 ) . The disadvantage neces- 
sarily incident to the use of iodine as a carrier is, that the reaction- 
product is easily contaminated with iodine derivatives, — in small 
quantities, it is true. 

In an entirely different way the chlorination is facilitated by the 
addition of red phosphorus. In this case, phosphorus pentachloride 
is first formed from the phosphorus and chlorine ; this, acting on the 
acetic acid, generates acetyl chloride, and this latter, with an excess 
of the acid, forms the anhydride. Direct experiments have shown that 
acid-chlorides, as well as anhydrides, are substituted by chlorine with 
much greater ease than the corresponding acids ; in this fact the action 
of red phosphorus finds its explanation. Since a small amount of 
phosphorus is sufficient for the chlorination of a large amount of acetic 
acid, the question as to how this is continuously effected remains to be 
answered. In accordance with the above statements, the following 
reactions take place : 

(1) P + C1 5 = PC1 5 

(2) CH 3 .CO.OH + PCl 5 = CH 3 .CO.Cl + POCl 3 + HC1 

CH 3 .CO\ 

(3) CH„.CO.Cl + CH 3 .CO.OH= >0 + HC1 

CH,.CO/ 



142 SPECIAL PART 

If the chlorine now acts on the anhydride, monochloracetic anhydride 
is formed : 

(4) CH 3 .CO\ CHoCl.CCK 

>0 + Cl 2 = " >0 + HC1 

CHg.CO/ CHg.CO/ 

But this reacts directly with the hydrochloric acid, in accordance with 
this equation : 

(5) CH 2 Cl.CO\ 

>0 + HC1 = CH.,Cl.CO.OH + CH-.CO. CI 



There is thus obtained, besides the molecule of chloracetic acid, the 
molecule of acetyl chloride, first formed in reaction 2, which is utilised 
repeatedly by its regeneration in accordance with reactions 3, 4, and 5. 

As a substitute for red phosphorus, sulphur is also recommended 
for the chlorination of aliphatic acids. This acts in a wholly similar 
manner, since it first forms sulphur chloride, which, reacting on the 
acid, like phosphorus chloride, converts it into an acid-chloride. The 
other phases of the reaction are similar to those given above. 

The bromination of aliphatic carbonic acids, which is not only 
of great importance in preparation work, but also as a means for 
determining constitution, is also conducted with the addition of red 
phosphorus (Hell-Volhard-Zelinsky Method). 1 

The halogen atoms always enter the a-position to the carboxyl 
group. Thus, e.g., when proprionic and butyric acids are brominated, 
they yield : 

CH3.CHBr.CO.OH CH 3 .CH 2 .CHBr.CO.OH 

a-Bromproprionic a-Brombutyric acid 

If no a-hydrogen atom is present, e.g., in trimethyl-acetic acid 
(CH 3 )o.C.CO.OH, bromination will not take place. The ability of 

an acid to form a bromine substitution product can, therefore, be used 
as a test for the presence of an a-hydrogen atom. Iodine cannot be 
introduced directly into aliphatic acids like chlorine and bromine. To 
obtain iodine substitution products, it is necessary to treat the corre- 
sponding chlorine or bromine compound with potassium iodide : 

CH 2 C1 . CO . OH + KI = CH 2 I . CO . OH + KC1 

The halogen derivatives of the fatty acids are in part liquids, in part 

1 B. 14, 891 ; 21, 1726; A. 242, 141 ; B. 21, 1904; B. 20, 2026; B. 24, 2216. 



ALIPHATIC SERIES 143 

solids. In their reactions they resemble the acids, on the one hand, 
since they form salts, chlorides, anhydrides, esters, etc. ; on the other 
hand, the halogen alkyls. They are of great value in the preparation 
of oxy- and amido-acids, of unsaturated acids, for the synthesis of poly- 
basic acids, etc. Below are given a few equations capable of general 
application : 

CH 2 Cl.CO . OH + H 2 = CH,(OH).CO. OH + HC1 

Oxyacetic acid = 
Glycolic acid 

CH 2 C1 . CO . OH + NH 3 = CH 2 . NH, . CO . OH + HC1 

Amidoacetic acid = 
Glycocoll 

CHJ CH 9 

i ir 

CH + KOH =CH + KI + H 2 

I \ I 

COOH CO. OH 

Acrylic acid 

CH 2 C1 . CO . OH + KCN = CH 2 . CN . CO . OH + KC1 

Cyanacetic acid 

CO. OH 

I 

CH., 
2 CH 2 Br . CO . OH + Ag, = | +2 AgBr 

CH, 



c 



O.OH 

Succinic Acid 



8. REACTION: OXIDATION OF A PRIMARY ALCOHOL TO AN 
ALDEHYDE 

Example : Acetaldehyde from Ethyl Alcohol l 

A ii-litre flask containing no grammes of concentrated sul- 
phuric acid and 200 grammes of water is closed by a two-hole 
cork ; through one hole passes a dropping funnel, through the 
other a glass delivery tube connected with a long condenser. To 
the lower end of the condenser is attached an adapter bent down- 
wards, the narrower portion of which passes through a cork in 



1 A. 14, 133 ; J. 1853, 329. 



144 



SPECIAL PART 



the neck of a thick-walled suction flask of about J-litre capacity. 
(See Fig. 65, page 128.) By using an upright coil condenser con- 
nected directly with the suction flask, an adapter is unnecessary. 
The suction flask is placed in a water-bath filled with a freezing 
mixture of ice and salt. The larger flask is heated over a wire 
gauze until the water just begins to boil ; a solution of 200 grammes 
of sodium dichromate in 200 grammes of water which has been 
treated with 100 grammes of alcohol is then added in a small 
stream through the dropping funnel, the lower end of which is 
about 3 cm. above the surface of the liquid in the flask. During 

the addition of the mixture, it 
will be unnecessary to heat the 
flask, since the heat produced 
by the reaction is sufficient 
to cause ebullition. The alde- 
hyde thus formed distils into 
the receiver, besides some al- 
cohol, water, and acetal. If 
uncondensed vapours of the 
aldehyde escape from the re- 
ceiver, the mixture is admitted 
to the flask more slowly. On 
the other hand, if boiling is not caused by the flowing in of the 
mixture, the reaction is assisted by heating with a small flame. 
After all of the mixture has been added, the flask is heated for a 
short time by a flame, until boiling begins. 

Since the aldehyde cannot be obtained easily from the reaction- 
products by fractional distillation, it is first converted into alde- 
hyde-ammonia, which, on proper treatment, readily yields the 
pure aldehyde. 

The apparatus for this purpose is arranged as follows : A small 
flask to contain the aldehyde, placed on a wire gauze, is connected 
with a moderately large reflux condenser. Into the upper end 
of the condenser is placed a cork bearing a r j_-shaped glass tube, 
which is connected with two wash-bottles, each containing 50 c.c. 
of dried ether. After the condenser has been filled with water at 




Fig. 66. 



ALIPHATIC SERIES I45 

30 (the lower side-tube of the condenser is closed with rubber 
tubing and a pinch-cock), the crude aldehyde is heated for 5-10 
minutes to gentle boiling, and the aldehyde that is not condensed 
passes over, and is absorbed by the ether. Should the ether begin 
to ascend in the connecting tube, the flame must be somewhat 
increased immediately. To obtain aldehyde-ammonia, a current 
of dry ammonia (see page 348) is conducted, with the aid of a 
wide adapter or funnel (Fig. 66), into the ethereal solution con- 
tained in a beaker surrounded by a freezing mixture of ice and salt, 
until the liquid smells strongly of it. After an hour, the aldehyde- 
ammonia which has separated out is scraped from the sides of the 
vessel and adapter with a spatula or knife, filtered with suction, 
washed with a little ether, and then allowed to dry on filter-paper 
in a desiccator. Yield, about 30 grammes. 

In order to obtain pure aldehyde, 10 grammes of aldehyde- 
ammonia are dissolved in 10 grammes of water, treated with a 
cooled mixture of 15 grammes of concentrated sulphuric acid 
and 20 grammes of water, and heated on the water-bath. Since 
aldehyde has a low boiling-point (21 ), the receiver is connected 
with the condenser by a cork, and well cooled with ice and salt. 

Aldehydes can be obtained by the use of the general reaction, which 
in many cases serves as a method of preparation, of extracting two 
hydrogen atoms from a primary alcohol by oxidation. 

CH3.CH0.OH + = CH 3 .C/ + H 

The name of the class of compounds is derived from this action : Alde- 
hyde = Al(cohol)dehyd (rogenatum). As an oxidising agent in the 
above case, chromic acid is the most suitable in the form of potassium, 
or sodium dichromate in the presence of sulphuric acid : 

Na 2 Cr 2 7 + 4 H 2 S0 4 = O g + (S0 4 ) 3 Cr 2 + Na 2 S0 4 + 4 H 2 

The rather difficultly soluble potassium dichromate (1 part dissolves in 
10 parts water) was formerly generally used, but at present the more sol- 
uble and cheaper sodium salt (1 part dissolves in 3 parts of water) is em- 
ployed wherever it is possible. But in the preparation of the simplest 
aldehyde (formaldehyde) from an alcohol a different oxidising agent is 



146 SPECIAL PART 

used, viz. the oxygen of the air. On passing a mixture of the vapour 
of methyl alcohol and air over a heated copper spiral, formaldehyde is 
produced. 

While by the first reaction one proceeds from substances which in 
comparison with the aldehydes are oxidation products of a lower order, 
the aldehydes may also be obtained by a second method involving the 
use of compounds of the same substitution series, viz. the dihalogen 
derivatives of the hydrocarbons containing the group CHC1 2 or CHBr 2 . 
If these are boiled with water, or, better, water containing sodium car- 
bonate, potash, lead oxide, or calcium carbonate, etc., the two halogen 
atoms are replaced by one oxygen atom : 

CH 3 .CHC1 2 + H,0 = CH3.CHO + 2HCI 

Ethylidene chloride 

C 6 H 5 .CHC1 2 + H 2 ±= C 6 H 5 .CHO + 2HCI 

Benzylidene chloride Benzaldehyde 

This method is used on the large scale for the manufacture of the com- 
mercially important benzaldehyde. It will be referred to under benzal- 
dehyde. 

Finally, aldehydes can be prepared from their oxidation products, 
the carbonic acids, by two methods, one of which has been already 
mentioned under acetic anhydride. If sodium amalgam is allowed to 
act on acid-anhydrides, an aldehyde is first formed : 

cH 3 .co\ 

>0 + H 2 = CH3.CHO + CH 3 .CO.OH 
CH3.CO/ 

But this reaction is of little practical value for the preparation of alde- 
hydes. The second method, which is the real preparation method, 
consists in the dry distillation of a mixture of the calcium or barium 
salt of the acid with calcium or barium formate : 

CH 3 . CO . Oca + H . CO . Oca = CH 3 . CHO + CaC0 3 
(ca = |Ca) 

The lower members of the aldehyde series are colourless liquids, soluble 
in water, possessing pungent odours. The intermediate members are 
also liquids, but insoluble in water ; the higher members are solid, crys- 
tallisable substances. The boiling-points of the aldehydes are lower 
than those of the corresponding alcohols. 



ALIPHATIC SERIES 147 

(CH3.CHO Boiling-point, 21 

1cH 3 .CH 2 .OH " « 78 

(CH 3 .CH 2 .CHO " "50° 

(CH 3 .CH 2 .CH,.OH .... " « 97 

Aldehydes are oxidised to acids by free as well as combined oxygen 
(compare benzaldehyde) : 

CH3.CHO + O = CH3.CO.OH 

Upon this action depends the fact that aldehydes cause metals to sepa- 
rate from certain salts, e.g. silver nitrate : 

CH 3 . CHO + Ag 2 = CH 3 . CO . OH + Ag^ 

Experiment : Treat a few cubic centimetres of a diluted silver 
nitrate solution with a few drops of ammonium hydroxide and 5 
drops of aldehyde. Silver will be deposited in the form of a brill- 
iant mirror on the walls of the vessel ; the deposition is especially 
beautiful if the vessel has previously been treated with a solution 
of caustic soda to remove any fatty matter. The reaction fre- 
quently takes place at the ordinary temperature, but in many 
cases only on gentle warming. The reaction is used for the 
detection of aldehydes. 

Another reaction which can also be employed for the recognition of 
aldehydes, depends upon the fact that they give a red colour to fuchsine- 
sulphurous acid. (Caro's reaction.) 

Experiment : Fuchsine-sulphurous acid is prepared by dissolv- 
ing fuchsine in water; a sufficient quantity of the latter is taken 
to prevent the solution from being too intense in colour. Sulphur 
dioxide is conducted into this until a complete decolouration takes 
place. To a few cubic centimetres of this solution add several drops 
of aldehyde. On shaking, a violet-red colour will be produced. 

Finally aldehydes may also be detected by a method depending upon 
the fact that when treated with diazobenzene sulphonic acid and sodium 
amalgam, they give a violet colour. 

Experiment : To as much diazobenzene sulphonic acid as can 
be held on the point of a knife, add 5 ex. of water, a few drops 

1 B. 15, 1635 and 1828. 



148 SPECIAL PART 

of caustic soda, and then a few drops of aldehyde, and finally a 
piece of solid sodium amalgam as large as a pea. After some 
time the red-violet colour appears. 

That aldehydes upon reduction pass over to primary alcohols has 
been mentioned under acetic anhydride : 

CHo.CHO + H 2 = CH 3 .CH 2 .OH 

It is wholly characteristic of the aldehydes that they unite directly 
(1) with ammonia, (2) sodium hydrogen sulphite, and (3) hydrocyanic 
acid. The union with ammonia takes place in accordance with the 
following equation : 

/OH 



CH...CHO + NE 



\NH 2 

Aldehyde-ammonia= 
a-amidoethyl alcohol 



This reaction is not so common as the second and third. Thus, 
e.g., formic aldehyde and most of the aromatic aldehydes behave 
differently toward ammonia. Whenever this reaction does take place 
it can also be used with advantage for the purification of the aldehyde, 
as in case of acetaldehyde ; by allowing the well-crystallised double 
compound to separate out, on treating it with dilute sulphuric acid, the 
free aldehyde is obtained. 

The union with sodium hydrogen sulphite takes place in accordance 
with the following equation : 

/OH 
CH3.CHO + SO.NaH = CHo.CHO 

\SO3Na 

Sodium-a-oxyethyl sulphonate 

This reaction may also be used for the purification of aldehydes, 
since when a concentrated solution of the sulphite is employed, the 
double compound generally separates out in a crystallised condition. 
The free aldehydes can be obtained from the sulphite compounds by 
heating with dilute acids or alkali carbonates. (Compare benzalde- 
hyde.) 

Experiment : Treat 5 c.c. of a cooled concentrated solution of 
sodium hydrogen sulphite with 1 c.c. of aldehyde and shake the 
mixture. The double compound separates out in a crystallised 
condition. 



ALIPHATIC SERIES 1 49 

As distinguished from the union of aldehyde with ammonia, this re- 
action is wholly general, and is frequently of great value in dealing with 
the aldehydes of the aromatic series. It should be noticed in this con- 
nection, that the ketones, which are closely related to the aldehydes, 
show similar reactions : 

CH 3 

CH3.CO.CH3 + S0 3 NaH = C<f 

Acetone \SO3Na 



The addition of hydrocyanic acid to ketones as well as to aldehydes 
is also general : 

/OH 
CH3.CHO + HCN = CH 3 .CH< 

\CN 

oL-oxyproprionitrile 

This reaction is of especial interest, since the addition of a new 
carbon atom is brought about. Concerning the value of this reaction 
for the synthesis of a-oxyacids, see Mandelic Nitrile, page 279. 

Aldehydes possess further a marked tendency to combine with them- 
selves (polymerise). 

Experiment : Treat 1 c.c. of aldehyde with one drop of con- 
centrated sulphuric acid. The aldehyde boils, and polymerisation 
(condensation) takes place. 

The compound thus obtained is called paraldehyde ; it boils much 
higher (124 ) than ordinary aldehyde; the determination of its vapour 
density shows that one molecule is composed of three molecules of 
ordinary aldehyde. Paraldehyde does not show the characteristic alde- 
hyde reactions ; on distillation with dilute sulphuric acid it is converted 
back into the ordinary variety. For this reason it is believed that no 
new union of carbon atoms takes place in the molecule, but that three 
molecules are united by means of the oxygen atoms : 

O - CH— CH 3 
CH 3 .CH<^ No 

O - CH— CH 3 

If aldehyde is cooled and treated with sulphuric acid, or if at the 
ordinary temperature gaseous hydrochloric acid, sulphur dioxide, or 
other compounds are passed into it, a solid polymerisation product, 



150 SrECIAL PART 

metaldehyde, is formed; this can also be converted back into the ordi- 
nary variety. 

The aldehydes undergo a wholly different kind of polymerisation 
under certain conditions, concerning which reference must be made to 
the chemical literature and treatises. For example, two molecules of 
acetaldehyde can unite with the formation of a compound in which a 
new carbon union is present. 

CH3.CHO + CH3.CHO = CH 3 .CH(OH).CH 2 .CHO 

Aldol 
This compound, as distinguished from paraldehyde and metaldehyde, 
is a true aldehyde, in that it cannot be converted back to acetalde- 
hyde. Aldol loses water easily, and is converted into an unsaturated 
aldehyde : 

CH 3 .CH(OH).CH 2 .CHO = CH 3 . CHzzCH.CHO 

Crotonaldehyde 

In connection with these condensations, it may be pointed out that 
many aldehydes, when heated with alkalies, polymerise to resinous 
products of high molecular weight (aldehyde resins). 

Experiment : Treat a few cubic centimetres of caustic potash 
solution with several drops of aldehyde, and warm. A yellow 
colouration takes place with the separation of a resinous mass. 

In order, finally, to represent the great activity of the aldehydes, the 
following equations are given : 

CH 3 . CHO + PC1 5 = CHj . CHC1 2 + POCl 3 

Ethylidene chloride 

CH3.CHO + NH 2 .OH =CH 3 .CH=NOH + H 2 

Aldoxime 

CH 3 . CHO + NH 2 . NH . C 6 H 5 = CH 3 . CH— N . NH . C 6 H, + H 2 

Phenylhydrazine Hydrazone of aldehyde 

OC 2 H 5 
CH 3 .CHO + 2C 2 H 5 .OH =CH 3 .CH<' + H 2 

OC 2 H 5 

Acetal, the ether of aldehyde- 

hydrate CH 3 . CH <^ qtt which does 

not exist in the free condition 



/ C 6 H 5 

CH..CHO + 2C 6 H 6 =CH 3 .CH/ + H 2 

X C 6 H 5 

Diphenyl ethane 



ALIPHATIC SERIES 151 



9. REACTION: PREPARATION OF A PRIMARY AMINE FROM AN 
ACID-AMIDE OF THE NEXT HIGHER SERIES 

Example : Methyl Amine from Acetamide l 

To a mixture of 25 grammes of acetamide, which has been 
previously well pressed out on a porous plate, and 70 grammes 
(23 c.c.) of bromine contained in a J-litre flask, add a solution of 
40 grammes of caustic potash in 350 c.c. of water (the flask is well 
cooled with water), until the brownish red colour formed at first is 
changed to a bright yellow, for which the greater portion of the 
potash solution will be required. This reaction-mixture is then, 
in the course of a few minutes, allowed to flow from a dropping 
funnel in a continuous stream into a litre flask containing a solution 
of 80 grammes of caustic potash in 150 c.c. of water heated to 
70-75 . In case the temperature rises higher than 75 , the flask 
must be cooled by immersion for a short time in cold water. The 
liquid is maintained at this temperature until it becomes colourless, 
which usually requires a quarter to half hour. The methyl amine 
is then distilled off with steam, and collected in a receiver contain- 
ing a mixture of 60 grammes of concentrated hydrochloric acid 
and 40 grammes of water. In order that the methyl amine may 
be completely absorbed by the acid, the end of the condenser is 
connected with an adapter which dips 1 cm. below the surface of 
the liquid in the receiver. If a coil condenser is employed, the 
end of it dips directly into the acid. As soon as the liquid in the 
condenser no longer shows an alkaline reaction, the distillation is 
discontinued. The methyl amine hydrochloride is partially evapo- 
rated in a porcelain dish over a free flame, then to dryness on the 
water-bath, and is finally heated for a short time in an air-bath at 
ioo° to dusty dryness. In order to separate the methyl amine 
salt from the ammonium chloride mixed with it, the finely pul- 
verised substance is crystallised from absolute alcohol, and the 
crystals separating out dried in a desiccator. Yield, varying. 

1 B. 15, 762 ; B. 17, 1406 and 1920. 



152 SPECIAL PART 

Under the discussion of acid-amides, it has already been mentioned 
that the hydrogen of the amido group (NH 2 ) can be substituted by 
bromine. If a 10 % solution of caustic potash is added to a mixture 
of one molecule of the amide and one molecule of bromine, until the 
brownish red colour of the latter has vanished, a monobromamide is 
formed, e.g., in the above case, acetmonobromamide in accordance 
with this equation : 

CH 3 . CO . NH 2 + Br 2 + KOH - CH 3 . CO . NHBr + KBr + H 2 

The monobromamide may be isolated in pure condition in the form 
of colourless, hydrous crystals. If hydrobromic acid is abstracted, 
no water being present, the position of the carbonyl group (CO) is 
changed, and an ester of isocyanic acid is formed : 

CH 3 . CONHBr = CH 3 . NzzCO + HBr 

Methyl isocyanate 

If the attempt is made to eliminate hydrobromic acid in the presence 
of water by the use of caustic potash solution, the above reaction takes 
place, but the isocyanate is unstable in the presence of alkalies, and 
decomposes immediately by taking up the water forming carbon dioxide 
and a primary amine : 

CH 3 .NCO + H 2 = C0 2 + CH 3 .NH 2 

Methyl amine 

This reaction, discovered by A. W. Hofmann, is, therefore, in its last 
phase, identical with the historical reaction of Wurtz, which led him, 
in 1848, to the discovery of the primary amines. 

The Hofmann reaction is capable of general application. By use of 
it, the primary amine of the next lower series may be obtained from 
any acid-amide, since the elimination of carbon dioxide takes place. 
With the higher members of the series, the reaction in part proceeds 
still further, since the bromine acts upon the primary amine to form a 
nitrile : 

C 7 H ]3 .CH 2 ,NH 2 + Br 4 + 4NaOH = C 7 H 15 .C=N + 4NaBr + 4H 2 

Octyl amine Octonitrile 

There is thus obtained from the higher members (compounds having 
five or more carbon atoms) of the amides, first the primary amine, and 
secondly, the nitrile of the next lower acid. In the aromatic series, the 
reaction for the preparation of primary amines, which contain the amido 
group in the benzene ring, is not of general importance, since these 

L 



ALIPHATIC SERIES 1 53 

may be obtained from the easily accessible nitro-compounds ; and 
since, on the other hand, if the above reaction is employed, bromine 
substitution products are easily formed. But in those cases in which 
the nitro-compound corresponding to the amine is not known, or can 
be prepared only with difficulty, the reaction is also of importance in 
the aromatic series. Two cases of this kind may be mentioned in this 
place. If phenyl acetamide is treated in accordance with Hofmann's 
reaction, there is formed in the usual way benzyl amine : 

C 6 H 5 . CH 2 . CO . NH 2 + O = C 6 H 5 . CH 2 . NH 2 + C0 2 

Phenyl acetamide Benzyl amine 

Further, the reaction is of practical value in the preparation of o-amido- 
benzoic acid, used in the manufacture of artificial indigo. If, as above, 
bromine and caustic potash are allowed to act on phthalimide, there is 
first formed, by the addition of water, an acid-amide : 

/CO\ /CO.NH 2 

o-C 6 H 4 < >NH + H 2 = C 6 H 4 < 

\CCK \CO.OH 

which in accordance with the following reactions gives the amido-acid. 

/CO.NH 2 /CO.NHBr 

C 6 H 4 < +Br 2 =C 6 H 4 < +HBr 

\CO.OH \CO.OH 

/CO . NHBr /N=CzzO 

C 6 H 4 < = C 6 H 4 < + HBr 



>CO.OH \CO.OH 

-N=C=0 /NHo 

4X + H 2 = C 6 H 4 < 

\CO.OH \CO.OH 



/1NZZUZIU /J 

C 6 H 4 < + H 2 = C 6 H 4 < + CO2 



Since the nitro-acid corresponding to the o-amido benzoic acid is diffi- 
cult to obtain, and phthalimide is easily prepared, the Hofmann reaction 
in this case gives a very convenient method of preparation for the 
amido-acid. 

Primary aliphatic amines can also be prepared according to the fol- 
lowing equations : 

(1) By the action of alcoholic ammonia on halogen alkyls : 

CH3I + NH 3 = CH 3 .NH 2 + HI 

In this case, secondary and tertiary bases, or the corresponding ammo- 
nium compounds, are also formed. 



154 SPECIAL PART 

(2) From alcohols and zinc chloride-ammonia : 

C 2 H 5 .OH + NH 3 = C 2 H 5 .NH 2 + H 2 

(3) By the reduction of nitriles (Mendius' reaction) : 

CH 3 .CN + 2H 2 = CH 3 .CH 2 .NH 2 

(4) By the reduction of nitro-compounds : 

CH 3 .N0 2 + 3H 2 = CH 3 .NH 2 + 2H 2 

(5) By the reduction of oximes and hydrazones : 

CH v CH=N.OH + 2H 2 = CH 3 XH 2 .NH 2 + H 2 

Acetaldoxime 

CH 3 . CH=N - NH . C 6 H 5 + 2 H 2 = CH 3 . CH 2 . NH 2 + C 6 H 5 . NH 2 

Ethylidene phenyl hydrazone Aniline 

The lowest members of the amines in the free condition are gaseous 
compounds soluble in water, possessing odours suggestive of ammonia : 
they differ from ammonia in being inflammable. 

Experiment : Treat some solid methyl amine hydrochloride in 
a small test-tube with a concentrated solution of caustic potash, or 
caustic soda, and warm gently. A gas, smelling like ammonia, is 
evolved, which burns with a pale flame. 

The higher members are liquids or insoluble solids. Since they are 
derivatives of ammonia, they possess basic properties, and, like ammo- 
nia, unite with acids to form salts, the composition of which is analo- 
gous to that of the ammonium compounds : 

NH 3 . HC1 ^ CH 3 . NH 2 . HC1 

(NH 4 Cl) 2 PtCl 4 ^(CH 3 .NH 2 .HCl) 2 PtCl 4 

NH 4 C1, AuCl 3 ^CH 3 .NH 2 .HC1, AuCL, 

The hydrochlorides of organic bases are distinguished from ammonium 
chloride by their solubility in absolute alcohol. Use was made of this 
property above. 

The numerous reactions of the primary amines need not be men- 
tioned here, since, under the aromatic amines, frequent reference will 
be made to them. At this place, one difference between the aromatic 
and aliphatic amines will be pointed out. If nitrous acid is allowed to 



ALIPHATIC SERIES I 55 

act on an aliphatic primary amine, an alcohol is formed with evolution of 
nitrogen : ^ _ NR ^ + N00H = £ Hg . OH + N 2 + H.,0 

while, under these conditions, an aromatic amine is converted into a 
diazo-compound (see Diazo-compounds). 

10. REACTION: SYNTHESES OF KETONE ACID-ESTERS AND 
POLYKETONES WITH SODIUM AND SODIUM ALCOHOLATE 

Example: Acetacetic Ester from Acetic Ester and Sodium 1 

For the successful preparation of acetacetic ester, the character 
of the acetic ester used is of great importance, since, if it is com- 
pletely free from alcohol, it will be attacked very slowly by sodium, 
even on heating ; if, on the other hand, it contains too much alco- 
hol, the sodium acts easily, but the yield of the product is varying 
and usually small. According to the experiments of the author, 
the following method of procedure gives a good yield and is one 
that does not fail. 

Purification of Acetic Ester : The acetic ester prepared accord- 
ing to Reaction 6, even after it has been freed from acetic acid 
and alcohol by shaking with sodium carbonate and calcium chloride 
respectively, dried over calcium chloride, and finally rectified, is 
not suitable for this preparation, since it reacts too violently with 
sodium. But if it is allowed to stand, after distilling, for some 
hours, over night at least, in a well-closed flask, over about \ its 
volume of granulated calcium chloride, and is then filtered, it may 
be used for the successful preparation of acetacetic ester. 

If commercial acetic ester is to be used, it must be shaken with 
a sodium carbonate solution, as described on page 137, treated 
with calcium chloride solution, etc. ; in short, it is treated as the 
crude product obtained in the preparation of acetic ester. Ob- 
viously, it is also necessary to allow it to stand over night in 
contact with calcium chloride, after the distillation. 

The yield of acetacetic ester may be further increased if the 
acetic ester, after being filtered from the calcium chloride, is again 
distilled, care being taken to prevent the absorption of moisture. 
All parts of the apparatus must be perfectly dried, and the end of 

1 A. 186,214. 



156 SPECIAL PART 

the condenser tube must be connected to the receiver (suction- 
flask) by a good cork. 

Preparation of Acetacetic Ester: 25 grammes of sodium from 
which the outside layers have been removed are cut with the aid 
of a sodium knife (Fig. 89) into pieces as thin as possible, and 
placed in a dry litre-flask. After this is connected with a long 
reflux condenser, inclined at an oblique angle, 250 grammes of 
dried acetic ester is poured into the top of the condenser, by a 
funnel which must not be attached to the condenser, but is 
held in the hand, so that the air may escape. If the acetic ester 
is added properly, no violent ebullition will occur, but at first a 
gradual, gentle boiling. After 10 minutes, the flask is placed on 
a previously heated water-bath, the temperature of which is so 
regulated that the acetic ester boils but gently; the reaction- 
mixture is heated until all the sodium is dissolved, which will 
require from 3-4 hours. To the warm liquid is added a mixture 
of 80 grammes of glacial acetic acid and 80 grammes of water, 
until it just shows an acid reaction. If a thick, porridge-like 
mass should separate out, this is again dissolved by vigorous 
shaking, or carefully breaking up the small lumps with a glass 
rod. To the liquid is then added an equal volume of a cold 
saturated solution of sodium chloride, and the lower aqueous layer 
is separated from the upper one, consisting of acetic ester and 
acetacetic ester, by allowing it to run off from a dropping funnel. 
Should a precipitate settle out on the addition of the salt solution, 
it is dissolved by adding some water. To separate the acetacetic 
ester from the main portion of the excess of the acetic ester used, 
the mixture is distilled from a flask, heated by a free flame over 
a wire gauze, or, more conveniently, without the wire gauze, with a 
luminous flame. As soon as the thermometer indicates 95 , the 
heating is discontinued, and the residue is subjected to vacuum- 
distillation, as described on page 25 . In place of the usual con- 
denser, the outside jacket of a Liebig condenser is pushed over 
the long side-tube of the distillation flask, and water is allowed 
to circulate through it. The heating is done in an air-bath. 
After small quantities of acetic ester, water, and acetic acid have 



ALIPHATIC SERIES 1 57 

passed over, the temperature becomes constant, and the main 
portion of the acetacetic ester distils over within one degree. 
The following table gives the boiling-points at various pressures. 
A reference to this will show at what approximate points the col- 
lection of the preparation should begin : 



ing-point 


71 at 12.5 


mm. 


pressure 


a 


74° " 14 


u 


u 


a 


79° " 18 


tt 


u 


tt 


88° « 29 


a 


a 


tt 


94° " 45 


a 


a 


a 


97° " 59 


a 


tt 


tt 


ioo° " 80 


a 


a 



The yield of acetacetic ester amounts to 55-60 grammes. 

In the preparation of this substance, it must be borne in mind 
that the experiment must be completed in one day. The opera- 
tion should be begun in the morning, the acetic ester heated with 
sodium at midday, and the experiment completed in the afternoon. 
If the reaction is discontinued at any point, and the unfinished 
preparation allowed to stand over night, the yield is essentially 
diminished. 

The formation of acetacetic ester from acetic ester, discovered by 
Geuther in 1863, takes place in accordance with the following equation : 



CHo.CO OC 9 H 



= CH 3 .CO.CH 2 .COOC 2 H 5 + C 2 H 5 .OH 

Acetacetic ester 

But the mechanism of the reaction is much more complicated than 
here indicated. According to the views of Claisen, the sodium first 
acts on the alcohol, which, as above mentioned, must be present in 
small quantities, forming sodium alcoholate, and this unites with the 
acetic ester as follows : 

A 

^ONa 



OC 9 H 5 
:H 3 .CO.OC 2 H 5 + C 2 H 5 .ONa = CH 3 .C^OC 2 H 5 



Reaction then takes place between this addition product and a second 
molecule of acetic ester, with the elimination of two molecules of alcohol, 
and the formation of the sodium salt of the acetacetic ester : 



158 SPECIAL PART 



.OC 2 H, Hk 

' >CH.CO.OC 9 H 5 
OC 2 H 5 + H/ 



ONa = CH 3 .C=CH . CO . OC 2 H 3 + 2 C 2 H 5 . OH 

ONa 

On acidifying with acetic acid, the sodium salt is decomposed with 
the formation of the free ester, CH 3 . CmCH . CO . OC 2 H 5 (enolform), 

OH 

which spontaneously changes into the desmotropic form (ketoform). 1 
CH 3 .CO.CH 2 .CO.OC 2 H 5 . 
In the form indicated above, the reaction is not capable of general 
application ; but a reaction closely related to it, discovered by Claisen 
and W. Wislicenus, is of general applicability, and is of great value in 
synthetical operations ; for this reason it will be briefly mentioned 
here. If sodium alcoholate is allowed to act on a mixture of the esters 
of two monobasic acids, a ketone acid-ester, having a constitution anal- 
ogous to that of acetacetic ester, is formed by the action of the sodium 
alcoholate on one of the esters with the elimination of alcohol, e.g. : 

C 6 H 5 .CO 



OC 2 H 5 + H| CH 2 . COOC 2 H 5 

Benzoic ester Acetic ester 

= C G H 5 . CO . CH 2 . CO . OC 2 H 5 + C 2 H 5 . OH 

Benzoyl acetic ester 

If one of the compounds is formic ester, esters of aldehyde-acids will 
be obtained, e.g. : 



H.CO 



OCoH, + H 



CH 2 . CO . OC 2 H 5 = H . CO . CH 2 . CO . OC 2 H 3 

Formic ester Acetic ester Formyl acetic ester 

If one molecule of a dibasic ester is used, a ketone dicarbonic acid 
ester will be formed, e.g. : 



OQH 5 H .CH 2 .CO.OC 2 H 5 CO.CH 2 .CO.OC 2 H 5 

~— Z -I '+C H s .OH 



CO. 

I 

CO.OC 2 H 5 

Oxalic ester Acetic ester Oxalacetic ester 

In place of the acid-ester in the above reaction, which is susceptible 
of many combinations, a ketone may be used; a ketone acid-ester is 
not formed, it is true, but polyketones, or ketone-aldehydes : 



CHo.CO 



Acetic ester Acetone 

= CH 3 . CO . CH 2 . CO . CH 3 + C 2 H 5 . OH 

Acetylacctone 



1 B. 31, 205, and 601. 



ALIPHATIC SERIES I 59 



C 6 H 5 . CO ;OC 2 H., + H.| CH, . CO . CH 3 

Benzoic ester = C 6 H 5 . CO . CH, . CO . CH 3 + C 2 H 5 . OH 

Benzoylacetone 



H.CO'OC,H 5 + H 



CH 2 .CO.C 6 H s 

Formic ester Acetophenone 

= 0=CH . CH 2 . CO . C 6 H 5 + C 2 H 5 . OH 

Benzoylaldehyde 

These few examples are sufficient to show the many-sided applica- 
tions of the above reaction. 

The most remarkable characteristic of acetacetic ester is that a portion 
of its hydrogen may be substituted by metals. If sodium is allowed to 
act on it, the sodium salt is formed with the elimination of hydrogen : 

CH 3 . CO . CHH . CO . OC,H 5 + Na = CH 3 . CO . CHNa . CO . OC,H 5 + H 

The same salt is also formed by shaking the ester with a solution of 
sodium hydroxide. The reason for this phenomenon is to be sought 
in the acidifying influence of the two neighbouring carbonyl (CO) 
groups. 

The synthetical importance of acetacetic ester depends on the fact 
that the most various organic halogen substitution products react with 
sodium acetacetic ester, the halogen uniting with the sodium, with the 
condensation of the two remaining residues. Thus a large number of 
compounds may be built up from their constituents. A few typical 
examples may elucidate these statements: 

(1) CH 3 .CO.CHNa.COOC 2 H 5 + ICH 3 

= CH 3 . CO . CH . CO . OC 2 H 3 + Nal 



Methylacetacetic ester 

(2) CH, . CO . CHNa . CO . OC 2 H 5 + C (i H, . CO . CI 

Benzoyl chloride 

= CH 3 . CO . CH - CO . OC 2 H 5 + NaCl 
CO 

I 

C 6 H 5 

Benzoylacetacetic ester 

(3) CH 3 . CO . CHNa . COOC 2 H 5 + CI . CH, . CO . OC 2 H 5 = 

Chloracetic ester 



CH 3 .CO.CH.CO.OC 2 H 5 

I 
CH, + NaCl. 



COOC,H 5 



Acetsuccinic ester 



160 SPECIAL PART 

In the compounds thus obtained the second methylene hydrogen 
atom is also replaceable by sodium, and this salt is likewise capable of 
entering into similar reactions, by which the number of derivatives is 
largely increased, e.g. : 

CH 3 .CO.C.Na-CO.OC 2 H 5 + IC 2 H s = CH 3 .CO.C— CO.OC 2 H 5 +NaI. 

CH 3 CH 3 C 2 H 5 

Sodiummethylacetacetic ester Methylethylacetacetic ester 

From all these compounds simpler ones may be obtained on saponi- 
fication. The acetacetic ester breaks up in one of two ways, depend- 
ing upon the conditions of the saponification : 



CH 3 .CO.CH 2 , 



CO.OC 2 H 5 + HOH = CH 3 .CO.CH 3 + C0 2 + C 2 H 5 .OH 

Acetone 



CH 2 .CO.OC 2 H 5 + HOH = 2CH 3 .CO.OH+ C 2 H 5 .OH. 

Acetic acid 

The first kind of decomposition is called " ketone decomposition," 
the second, "acid decomposition. 11 Since, as shown above, either one 
or both of the methylene hydrogen atoms in acetacetic ester can be 
replaced by different radicals, X or Y, these substances yield either 
mono- or di- substituted acetones : 

X \ 
X.CH 2 .CO.CH 3 and Vh.CO.CH 3 

as well as mono- and di- substituted acetic acids, 

X.CH 2 .CO.OH and ^CH.CO.OH. 

The variety of the acetacetic ester syntheses is still further increased 
by the fact that two molecules of the ester, by reaction with aldehydes 
or alkylene bromides, may be united with one another by the most 
various bivalent radicals. 

These examples are sufficient to show the value of acetacetic ester 
and analogous compounds for organic syntheses. Acetacetic ester 
may not only be employed for the syntheses of carbon compounds, but 
it also reacts with nitrogen compounds, e.g., aldehyde-ammonia, phenyl 
hydrazine, aniline, etc. This action will be referred to later in the 
appropriate places. 



ALIPHATIC SERIES l6l 



11. REACTION: SYNTHESES OF THE HOMOLOGUES OF ACETIC ACID 
BY MEANS OF MALONIC ESTER 

Example : Butyric Acid from Acetic Acid 

(a) Preparatiofi of Malonic Ester 

Dissolve 50 grammes of chloracetic acid in 100 grammes of 
water; warm gently (about 50 ), and neutralise with solid, dry, 
potassium carbonate, for which 30-40 grammes will be required. 
The solution is then heated gradually, with thorough stirring, while 
40 grammes of pure, finely pulverised potassium cyanide are added. 
(Use a sand-bath or asbestos plate, under the hood.) The forma- 
tion of cyanacetic acid takes place, with vigorous ebullition. When 
the reaction is complete, the mixture is evaporated as quickly as 
possible on the sand-bath until a thermometer placed in the vis- 
cous brownish salt indicates 135 . Since the substance "bumps" 
and spatters during the evaporation, it is constantly stirred with 
the thermometer, the hand being protected by a glove or cloth. 
It is allowed to cool, the stirring being continued during the cool- 
ing, otherwise the product bakes into a hard, scarcely pulverisable 
mass. It is then quickly powdered as finely as possible, placed in 
a ^-litre flask provided with a reflux condenser, and treated with 
20 c.c. of absolute alcohol. A cooled mixture of 80 c.c. of absolute 
alcohol and 80 c.c. of concentrated sulphuric acid is then added 
gradually, with good shaking, through the condenser tube. The 
pasty mass is now heated, with frequent shaking, two hours in 
a water-bath (hood) ; it is then well cooled, and treated with 150 
c.c. of water (shaking). After the undissolved salt has been filtered 
orT with suction, it is washed on the filter several times with ether. 
The filtrate, consisting of the water solution and the ether wash- 
ings, is then carefully extracted with a sufficiently large quantity 
of ether. The ethereal extract is shaken up in a separating funnel 
with a concentrated solution of sodium carbonate until it no longer 
shows an acid reaction. ( Owing to the copious evolution of gas the 
funnel is not closed at first.) It is then dried over fused Glauber's 



1 62 SPECIAL PART 

salt, and after the evaporation of the ether, distilled. Boiling- 
point, 1 95 . Yield, about 40 grammes. 

The compound may also be advantageously dried, without the 
use of Glauber's salt, by evaporating off the ether, and heating 
the residue about a quarter hour in a vacuum on a water-bath. 
(Compare page 49.) 

(b) The Introduction of an Ethyl Group 

Dissolve 2.3 grammes of sodium in 25 grammes of absolute 
alcohol in a small flask connected with a reflux condenser ; treat 
the cooled solution gradually with 16 grammes malonic ester, — 
the transparent crystals of sodium ethylate separating out at first 
pass over into a voluminous pasty mass of sodium malonic ester, — 
and then, with shaking, add through the condenser 20 grammes 
of ethyl iodide in small portions. The mixture is then heated on 
the water-bath until the liquid no longer shows an alkaline reac- 
tion, for which one or two hours may be necessary. The alcohol 
is then distilled off on an actively boiling water-bath, a thread. being 
placed in the flask to facilitate the boiling ; the residue is taken 
up with water and extracted with ether, the ether evaporated, and 
the residue distilled. Boiling-point, 206-208 . Yield, about 15 
grammes. 

(c) Saponification of Ethyl Malonic Ester 

For the saponification of the ester, a concentrated solution of 
caustic potash is prepared ; for every gramme of the ester, a 
solution of 1.25 grammes potassium hydroxide in 2 grammes of 
water is used. The cooled solution is placed in a flask provided 
with a reflux condenser ; through this the ester is gradually added ; 
an emulsion is first formed, which soon solidifies to a white solid 
mass, probably potassium ethylmalonic ester. On heating the mix- 
ture on a water-bath a sudden energetic boiling-up sets in, especially 
if the flask be shaken. The heat generated in the reaction causes 
the alcohol, liberated in the saponification, to boil. After about 
an hour's heating on the water-bath, the oily layer disappears, 
showing that the saponification is complete. 



ALIPHATIC SERIES 1 63 

The free ethyl malonic acid may be obtained by following either 
of the methods' given below : 

(1) The solution is diluted with ij times the volume of water 
previously used to dissolve the caustic potash. To this is added, 
gradually, with cooling, a quantity of concentrated hydrochloric 
acid equivalent to the total amount of caustic potash used (the 
strength of the acid is determined by a hydrometer). The ethyl- 
malonic acid liberated is taken up with not too little ether, the 
ethereal solution dried over anhydrous Glauber's salt, the ether 
evaporated, and the residue heated, with stirring, on a water-bath, 
in a large watch crystal or dish, until it begins to solidify. After 
cooling, it is pressed out on a drying plate and crystallised from 
benzene. Melting-point, 111.5 . Yield, about 7 grammes. 

(2) The solution is diluted with the same volume of water pre- 
viously used to dissolve the caustic potash. To this is added 
carefully and with cooling concentrated hydrochloric acid, until an 
acid reaction may just be detected. The ethyl malonic acid is 
precipitated out in the form of its difficultly soluble calcium salt, 
by the addition of a cold solution of calcium chloride, as concen- 
trated as possible. This is filtered off, well pressed on a porous 
plate, and the ethyl malonic acid liberated by treating carefully 
with concentrated hydrochloric acid is obtained pure as in (1). 

(d) Elimination of Carbon Dioxide from Ethyl Malonic Acid 

The ethyl malonic acid is placed in a small fractionating flask 
provided with a long condensing tube supported in an oil-bath at 
an oblique angle, so that its outlet tube is inclined upward. The 
mouth is closed by a cork bearing a thermometer. The acid is 
heated at 180 , until carbon dioxide is no longer evolved, which 
will require about a half-hour. The residue is distilled from the 
same flask in the usual way ; the butyric acid passes over between 
162-163 . Yield, about 80-90% of the theory. 

(a) In the first phase of the reaction which gives ethylmalonic ester, 
the potassium cyanide acts on trichloracetic acid, or on its potassium 
salt, with the formation of cyanacetic acid : 



1 64 SPECIAL PART 

CH 2 C1 . CO . OH + KCN = CH 2 . CN . CO . OH + KC1 

Cyanacetic acid 

As already mentioned in the preparation of acetonitrile, a halogen 
united with aliphatic residues may generally be replaced by the cyanogen 
group, on heating with potassium or silver cyanide. If alcohol and 
sulphuric acid or ethylsulphuric acid are now allowed to act on the 
cyanacetic acid, three reactions take place. At first there is an esterifi- 
cation in accordance with the equation : 

CH 2 .CN.CO.OH + C 2 H 5 .OH = CH 2 .CN.CO.OC 2 H 5 + H 2 

Cyanacetic ester 

Under the discussion of acetic ester, it has already been brought 
forward that, in general, acid esters can be obtained by treating a mix- 
ture of the alcohol and acid with sulphuric acid. In the second place, 
the sulphuric acid has a saponifying action on the cyanacetic ester, 
i.e., the cyanogen group is converted into carboxyl (COOH). 

CO. OH 

I 
CH 2 .CN.CO.OC 2 H 5 + 2 H 2 = CH 2 + NH 3 

CO.OC 2 H 5 

Acid ester of malonic acid 

The carboxyl group thus formed is then acted on in the same way 

as the carboxyl group of cyanacetic acid above, with the formation of 

an ester : 

CO. OH CO.OC 2 H 5 

I I 

CH 2 + C 2 H 5 . OH = CH 2 + H 2 

CO.OC 2 H 5 CO.OC 2 H 5 

Malonicdiethyl ester 

(J?) The ester of malonic acid, like acetacetic ester, possesses the 
property in virtue of which one of the two methylene hydrogen atoms 
can be replaced by sodium, in consequence of the acid properties im- 
parted by the two neighbouring carbonyl (CO) groups. When the 
sodium compound is treated with organic halides, like alkyl halides, 
halogen derivatives of acid-esters, acid-chlorides, etc., the sodium is 
replaced by alkyl residues, acid residues, etc., just as in the case of the 
closely related acetacetic ester. In the above-mentioned examples, the 
sodium salt of the malonic ester is first formed from sodium alcoholate 
and the ester : 



ALIPHATIC SERIES 



I6 5 



CO.OC 2 H 5 



CO.OC 2 H 5 



CH H + C,H..O Na = CHNa -f C 2 H 5 .OH 



CO.OC,H 5 CO.OC 2 H 5 

Ethyl iodide reacts on this as follows : 

CO.OC 2 H 3 CO.OC 2 H 5 



Na + I 



CH 

I 
CO. OCR 



CoH, 



+ NaI 



CO.OC 2 H 5 

Ethylmaionicdiethy] ester 

As in acetacetic ester, the second hydrogen of the malonic ester can 
also be replaced by sodium ; consequently the malonic ester is capable 
of reacting a second time with organic halides, so that disubstituted 
malonic esters can also be prepared. 

(c ) The compounds thus obtained of the general formulae : 
CO.OCH. 

I 

CH-X and C 
I I X Y 

CO.OC 2 H 5 CO.OQH. 

are distinguished from the corresponding derivatives of acetacetic ester 
in that on saponification they do not decompose, but yield the free 
substituted malonic acids. Thus, the ethylmalonicdiethyl ester reacts 
with caustic potash as follows : 

CO.OC,H 5 KOH CO. OK 

I I 



CH.C,H< 
I 



CH.C 2 H 5 + 2C 2 H 5 .OH 
CO. OK 



CO.OC 2 H 5 KOH 
(d) From the substituted malonic acid thus obtained, derivatives 
of acetic acid may be prepared by heating it to a high temperature. 
It is a general law that one carbon atom cannot hold two carboxyl 
groups in combination at high temperatures, since carbon dioxide will 
be eliminated from one. By this means, a dicarbonic acid is converted 
into a monocarbonic acid, e.g. : 



CO.O 



H 



I 

I " 
CO. OH 



H. 



CH, 

I 

CO. OH 



+ CO, 



1 66 SPECIAL PART 

From the mono- or di- substituted malonic acid a substituted acetic 
acid is obtained of the formula, 

CHo-X CH< 

| or | \Y 

CO. OH CO. OH 

Thus from ethylmalonic acid, there is formed ethylacetic acid = 
butyric acid. If, instead of ethyl iodide, methyl or propyl iodide 
is used, proprionic acid or valerianic acid respectively is obtained. 
If two methyl groups are introduced into malonic ester, then, on 
decomposition, a dimethylacetic or isobutyric acid will be formed. 

As shown above, similar acids may be prepared from the acetacetic 
ester. Since the decomposition of the acetacetic ester derivatives may 
take place in two different ways (acid- and ketone-decomposition) ; 
and since these decompositions frequently take place side by side, while 
the malonic acid derivatives decompose in only one way, so in most 
cases it is more advantageous to use the malonic ester for the synthesis 
of the homologous fatty acids. 

12. REACTION: PREPARATION OF A HYDROCARBON OF THE 
ETHYLENE SERIES BY THE ELIMINATION OF WATER FROM AN 
ALCOHOL. COMBINATION OF THE HYDROCARBON WITH BROMINE 

Example : Ethylene from Ethyl Alcohol. Ethylene Bromide 1 

A mixture of 25 grammes of alcohol and 150 grammes of con- 
centrated sulphuric acid is heated, not too strongly, in a litre 
round flask on a wire gauze covered with thin asbestos paper, or 
sand bath (Fig. 67). As soon as an active evolution of ethylene 
takes place, add, through a dropping funnel, a mixture of 1 part 
alcohol and 2 parts concentrated sulphuric acid (made by pouring 
300 grammes of alcohol into 600 grammes of sulphuric acid, with 
constant stirring), slowly, so that a regular stream of gas is 
evolved. If the mixture in the flask foams badly with a separa- 
tion of carbon, it has been too strongly heated, and it is advisable 
to empty the flask and begin the operation anew. In order to 
free the ethylene from alcohol, ether, and sulphur dioxide, it is 
passed through a wash-bottle containing sulphuric acid, and a 
second one, provided with three tubulures, the central one sup- 

1 A. 168, 64; A. 192, 144. 



ALIPHATIC SERIES 



167 



plied with a safety-tube, containing a dilute solution of caustic 
soda. It then enters two wash-bottles, each containing 25 c.c. of 
bromine, covered with a layer of water 1 cm. high. Since the 
combination of ethylene with bromine causes the evolution of heat, 
the bromine bottles are placed in thick-walled vessels filled with 
cold water. In order to get rid of the bromine vapours which 
escape from the last bottle, it is connected with the hood or with 
a flask containing a solution of caustic soda ; to prevent the caustic 
soda from being drawn back into the bromine bottle, the delivery 
tube must not dip under the surface of the caustic soda. As 
soon as the bromine is decolourised, the operation is discontinued, 
care being taken to disconnect all of the vessels immediately; 




Fig. 67. 
otherwise, in consequence of the cooling of the large flask, the 
contents of the bottles will be drawn back. The ethylene bromide 
is then washed repeatedly with water in a dropping funnel, and, 
finally, with caustic soda solution. It is dried over calcium 
chloride, and, on distillation, is obtained perfectly pure. Boiling- 
point, 130 . Yield, 125-150 grammes. 

The addition of the alcohol-sulphuric acid mixture is often at- 
tended with difficulty, in that as soon as the cock is opened, the gas 
passes out through the funnel, thus preventing the entrance of the 
mixture. This difficulty may be obviated by taking the precaution 
of always keeping the stem of the funnel filled with the mixture. 



1 68 SPECIAL PART 

Before the heating is begun, a portion of the mixture is placed in 
a porcelain dish, the end of the stem of the funnel immersed 
in it and filled by suction. The cock is then closed, the funnel 
placed in the cork of the generating flask, and the heating begun. 
The hydrocarbons of the ethylene series may be prepared, in general, 
by abstracting water from the corresponding alcohol, e.g. : 

CH 3 .CH 2 .OH = CH 2 =CH 2 + H 2 0. 

If sulphuric acid is used as the dehydrating agent, the reaction does 
not follow the above equation, but ethylsulphuric acid is first formed, 
and this, on heating, yields sulphuric acid again : 



•OH 

C 2 H 5 .OH + S0 2 = 
X)H 


/OC 2 H 5 
: S0 2 + H 2 
X)H 




Ethylsulphuric acid 


/OC 2 H 5 
S0 2 
\)H 


/OH 

C 2 H 4 + S0 2 . 

X)H 



In many cases the elimination of water takes place so easily that 
the use of concentrated sulphuric acid is unnecessary, since the diluted 
acid answers the purpose. With the higher members of the series the 
reaction is complicated by the fact that the simple alkylenes polymerise 
under the influence of sulphuric acid. Thus there is formed, besides 
butylene, C 4 H 8 , hydrocarbons having respectively twice and three times 
its molecular weight, e.g. : 

C 8 H ]6 Dibutylene 

C 12 H 24 Tributylene 

In these cases it is much more convenient to prepare an ester from 
the alcohol by the action of the chloride of a higher fatty acid, and 
subjecting this to distillation by which it is decomposed into an hydro- 
carbon of the ethylene series and the free fatty acid, e.g. : 

C li5 H, 1 .CO.OC 10 H,o = Cj.H^.CO.OH + C 1G H. {2 

Cetyl palmitate Palmitic acid Hexadecylene 

The first four members of the alkylene series are gases at ordinary 
temperatures, which burn with strongly luminous, smoky flames. The 



ALIPHATIC SERIES 1 69 

intermediate members are colourless liquids, not miscible with water, 
which can be distilled at ordinary pressures without decomposition ; 
the higher members are solids, and can only be distilled without de- 
composition in a vacuum. Chemically these compounds are charac- 
terised primarily by the property of uniting with two univalent atoms, 
or a univalent atom and a univalent radical, upon which the double 
union is changed to single union. 

They take up, especially in the presence of platinum-black, two 
atoms of hydrogen, thus passing over to the hydrocarbons of the satu- 
rated series (paraffins) : 

CH 2 zz CH 2 -f- H 2 

Hydrogen halides may also be added to them ; hydriodic acid with 
the greatest ease, hydrobromic acid with less, and hydrochloric acid 
only with difficulty : 

CH 2 zzCH 2 + HI = CH 3 .CH 2 I. 

Ethyl iodide 

The homologues of ethylene also form addition products ; the halo- 
gen atom seeks that carbon atom which is combined with the smallest 
number of hydrogen atoms : 

CH 2= CH.CH, + HI = CH 3 .CHI.CH 3 . 

Propylene Isopropyl iodide 

The constituents of water (H and OH) may also be added indirectly 
to the alkylenes. If concentrated sulphuric acid be allowed to act on 
one of them, it dissolves, forming a sulphuric acid ester : 

/OH /OC 2 H 5 
CH 2= CH 2 + S0 2 = S0 2 , 

X)H X 0H 

If this is boiled with water, the ester is decomposed into alcohol and 
sulphuric acid : 

/OC,H, ^OH 

S0 2 +HOH =C 2 H 5 .OH + S0 2 , 

\)H \)H 

so that finally H and OH have been added to ethylene : 
CH 2= CH 2 H- H.OH = CH 3 .CH 2 .OH. 



170 SPECIAL TART 

Analogous to the halogen atoms, the hydroxyl (OH) group unites 
with that carbon atom holding in combination the smallest number of 
hydrogen atoms. 

The alkylenes take up two atoms of chlorine or bromine with great 
ease : 

CH 2 -CH 2 + Cl 2 = CH 2 C1 - CH 2 C1 

CH 2 =CH 2 ± Br 2 = CH 2 Br - CH 2 Br. 

Finally they combine directly with hypochlorous acid to form glycol- 
chlorhydrines. 

The reactions taking place in the formation of the alkylenes as well 
as those in the formation of addition products are not only applicable 
to the hydrocarbons but also to their substitution products. Thus, 
e.g., unsaturated acids are commonly obtained from oxyacids by the 
elimination of water : 

CH 2 .OH.CH 2 .CO.OH = CH 2 zz CH.CO.OH + H 2 

/3-hydroxyproprionic acid Acrylic acid 

C 6 H 3 . CH . OH . CH 2 . CO . OH = C 6 H 5 . CH=CH . CO . OH -f H,0 

Phenyllactic acid Cinnamic acid 

All compounds in which the ethylene condition is present show the 
addition phenomena, in accordance with the following equations : 

CH 2 =zCH.CH 2 .OH + Br 2 = CH 2 Br - CHBr.CH 2 .OH 

Allyl alcohol Dibromhydrine 

CH 2 z=CH . CO . OH + Br 2 = CH 2 Br - CHBr. CO . OH 

Acrylic acid Dibromproprionic acid 

C G H 5 . CHzrCH .CO. OH + Br 2 = C 6 H 5 . CHBr - CHBr. CO . OH 

Cinnamic acid Dibromhydrocinnamic acid 

C G H 5 . CH=CH . CO . OH + HBr = C 6 H 5 . CHBr - CH 2 . CO . OH 

Bromhydrocinnamic acid 

C 6 H 5 .CH=CH 2 + Br 2 = QH,.CHBr - CH 2 Br, 

Styrene Styrene dibromide 

C 6 H 5 .CH— CHvC0.0H + C1.0H=C 6 H s .CH.0H.CHCl.C0.0H 

Phenylchlorlactic acid 

CH 2 =CH.CO.OH + H 2 = CH 3 .CH 2 .CO.OH. 

Acrylic acid Proprionic acid 



ALIPHATIC SERIES 171 

13. REACTION: REPLACEMENT OF HALOGEN ATOMS BY ALCOHOLIC 
HYDROXYL GROUPS 

Example : Ethylene Alcohol (Glycol) from Ethylene Bromide 
(a) Conversion of Ethylene Bromide into Glycoldiacetate 

A mixture of 60 grammes ethylene bromide, 20 grammes glacial 
acetic acid, and 60 grammes of freshly fused, finely pulverised 
potassium acetate, 1 placed in a 1-litre, short-necked, round flask, 
provided with a reflux condenser, is heated to active boiling for 
two hours on a sand-bath over a large flame. The reaction prod- 
uct is then distilled (with a condenser) over a large luminous 
"flame kept in continuous motion. Toward the end of the distilla- 
tion the flame is gradually made non-luminous. The distillate is 
then further treated with 60 grammes ethylene bromide and 80 
grammes potassium acetate, and the mixture, as above, heated to 
active boiling for two to three hours on a sand-bath. The re- 
action product is then again distilled over (with a condenser) by 
a luminous flame. The distillate is fractioned — using a 10 cm. 
long Hempel tube. The fractions are collected as follows : 1. up 
to 140 ; 2. from 140-175 ; 3. above 1 75°. Fractions 2 and 3 
are then again distilled separately. The pure glycoldiacetate 
goes over between 180-190 , the main portion at 186 . Yield, 
about 70 grammes. 

If it is desired to increase the yield, the portion going over 
under 180 is heated for three hours longer with potassium acetate. 
The product is then treated as above described. This causes an 
increase of about 15 grammes. 

{I?) Saponification of Glycoldiacetate 
A mixture of 50 grammes of glycoldiacetate and 35 grammes 



1 Potassium acetate (Kalium aceticum pur. Ph. G. III.), differing from sodium 
acetate (compare page 127), crystallises without water of crystallisation. Never- 
theless, for this experiment it must be heated to fusion over a free flame in an iron 
or nickel dish. The melted salt is poured into a shallow, flat iron or copper dish, 
in a thin layer. While still warm it is pulverised as finely as possible, and must be 
at once transferred to a bottle which is to be kept tightly closed. For this experi- 
ment 200 grammes of the salt are fused. 



172 SPECIAL PART 

of freshly slaked lime (dried at 150 in an air-bath), placed in a 
150 c.c. round flask, the walls of which are not too thin, provided 
with a short reflux condenser, is heated in an air-bath — tall iron 
crucible — for about four hours, at 170-180 ; the crucible is 
covered with an asbestos plate provided with a slit of the proper 
size. 

The glycol formed is obtained by a vacuum distillation. For 
this purpose the flask is connected with a tube — \ in. in length, 
not too wide, and bent downwards ; it is inserted into a short 
condenser. A 50 c.c. fractionation flask, with the side tube near 
the bulb, is employed as the receiver. 

After exhausting the apparatus as completely as possible, the. 
flask is heated in the air-bath (used in the saponification, closed 
with the asbestos plate) at first to 150 , toward the end to 200 , 
until no more glycol passes over. Since this is firmly retained by 
the calcium acetate, which finally becomes as hard as stone, the 
distillation, at times, must be continued from one to two hours, 
if a good yield of glycol is desired. In order to separate it from 
small quantities of the unsaponified ester, which cannot be done 
through distillation, owing to the slight' difference in their boiling- 
points, the viscous distillate in the fractionating flask is shaken up 
twice with an equal volume of dry ether ; the glycoldiacetate is 
taken up, while the glycol remains undissolved. The main por- 
tion of the ether is removed with a pipette, and the last portions 
by carefully heating the upper of the two layers of liquid. The 
glycol is then distilled over, the fraction distilling above 185 
being collected separately. Yield, 16-18 grammes. Boiling- 
point of the pure glycol, 195 . The boiling-point of the com- 
pound is somewhat lowered by a small quantity of water. 

This preparation shows a method for replacing a halogen atom by 
an alcoholic hydroxyl group. In Reaction 1 the reverse replacement 
was brought about, — the substitution of a hydroxyl group by a halogen. 
This method is obviously only of importance in those cases in which it 
is more convenient to obtain the halogen derivative than the alcohol. 
Among the monacid alcohols it is of value for preparing isopropyl 
alcohol, normal secondary butyl, and normal secondary hexyl alcohols. 



ALIPHATIC SERIES 173 

As stated on page 115, the action of hydriodic acid on polyacid alco- 
hols does not yield, as might be expected, the poly-iodine derivatives, 
but mono-iodine derivatives. Thus from glycerol, isopropyl iodide is 
obtained ; from erythrite, normal secondary butyl iodide ; from man- 
nite, the normal secondary hexyl iodide. These iodides, as pointed 
out, may be converted into the corresponding alcohols. The method 
is of practical value in the preparation of tertiary alcohols from acid- 
chlorides and zinc alkyls. — Butlerow 1 s synthesis. Compare page 126. 
In this reaction the tertiary chloride is formed as an intermediate 
product. The method is of importance for the preparation of di-acid 
alcohols (glycols), especially for the a-glycols, in which the hydroxyl 
groups are combined with the two adjacent carbon atoms. The 
dibromides corresponding to these alcohols are easily obtained by the 
addition of bromine to the hydrocarbons of the ethylene series. In 
this way glycol was first prepared by Wurtz. 1 

Other glycols may be obtained in a similar manner, e.g., if allyl 
bromide be treated with hydrobromic acid, trimethylene bromide is 
formed, from which a /^-glycol — trimethylene glycol — may be obtained 
by the above reaction. 

If, to unsaturated mono-acid alcohols containing a double union, two 
bromine atoms be added, dibrom-alcohols are obtained which, by re- 
placing the bromine with hydroxyl, yield tri-acid alcohols : 

CH2=CH.CH 2 Br + BrH = CH 2 Br.CH 2 .CH 2 Br — >- CH 2 (OH) .CH 2 .CH 2 (OH) 

Allyl bromide Trimethylene bromide Trimethylene glycol 



I I I 

CH CHBr CH(OH) 

II +Br 2 =| -^ I 

CH CHBr CH(OH) 

I I I 

CH 2 (OH) CH 2 (OH) CH,(OH) 

From these examples the value of this method for obtaining alcohols is 
evident. 

Oxyaldehydes, oxyketones, and oxyacids may also be obtained by this 
reaction, from the corresponding halogen compounds. Finally, it may 
be employed to replace the halogen, in side-chains of aromatic com- 
pounds, by hydroxyl. 

The substitution of halogen atoms by hydroxyl groups may be done 

1 A. ch. (3), 55, 400. 



CH 2 Br 


CH (OH) 


| + K 2 CO s + HoO : 


= I + co 2 


CH.Br 


CH 9 (OH) 



174 SPECIAL PART 

by two methods: (1) Directly in a single operation. (2) In two re- 
actions ; (a) by preparing an acid-ester of the desired alcohol, and 
(b) subjecting this to saponification. If method (1) be used, the halogen 
derivative is heated with water at the ordinary pressure, or if necessary, 
at an increased pressure. The same object is attained more quickly, 
and in many cases with a better yield, by the addition to the reaction- 
mixture of certain oxides, hydroxides, or carbonates. Silver oxide, lead 
hydroxide, barium hydroxide, potassium or sodium carbonate, and others 
may be used for this purpose. It appears to be true that a tertiary 
halogen atom reacts more easily than a secondary or primary, and that 
a secondary, more easily than a primary. By following this method, 
glycol may be obtained directly from ethylene bromide, if the latter be 
heated with water and potassium carbonate : 



2KBr 



The separation of the glycol from the large excess of water used is 
troublesome. 

In accordance with method (2) certain salts, as silver, potassium, or 
sodium acetate are allowed to act on the halogen substitution product. 
This results in the formation of an ester of the desired alcohol : 

CH.Br CH 9 .OOC.CH 3 

I + 2CH3.COOK = I ' + 2KBr 

CH 2 Br CH 2 .OOC.CH 3 

Glycoldiacetate 

The ester is then saponified under the proper conditions, upon which 
the free alcohol is obtained : 

CH,.OOC.CH 3 CH„(OH) 

I " +Ca(OH) 9 =| + (CH 3 .COO) 2 Ca 

CH 2 .OOC.CH 3 - CH 2 (OH) 

Glycol is a thick, colourless, odourless liquid, boiling at 195 ; it melts at 
1 1. 5 after having been solidified by low temperature. Like all poly- 
acid alcohols, it has a sweet taste. It is easily soluble in water and in 
alcohol, but not in ether. Chemically it differs only from the mono-acid 
alcohols in its ability to form mono- or di- derivatives according to the 
conditions : 



CH,.ONa CH 2 .ONa 


CH 9 .00C.CH.> CH,.OOC.CH, 


and | ; 


| "and | 


CH 2 .OH CH 2 .ONa 


CH„.OH CH,.OOC.CH. 



ALIPHATIC SERIES 1 75 

Both hydroxyl groups are replaced by the action of phosphorus penta- 
chloride : 

CH 2 (OH) CH 2 .C1 

I +2PC1 3 = I +2POCI3 + 2HCI 

CH 2 (OH) CH 2 .C1 

But if glycol be heated with hydrochloric acid, only one hydroxyl group 
is replaced : 

CH,(OH) CH 2 .C1 

I + HC1 =. I + H 2 

CH 2 (OH) CH,(OH) 

Ethylene chlorhydrine 

From these so-called halogen hydrines, by the action of alkalies the 
inner anhydrides of the glycols are obtained : 

CH 2 .C1 CPU 

I = I ">0 + HCl 

CH 2 .(OH) CH/ 

Ethylene oxide 



176 SPECIAL PART 



TRANSITION FROM THE ALIPHATIC TO THE 
AROMATIC SERIES 

Dimethylcyclohexenone and s-Xylenol from Ethylidenebisacetacetic 
Ester. (Ring Closing in a 1.5 Diketone. Knoevenagel Reaction. 1 ) 

1. ETHYLIDENEBISACETACETIC ESTER 

In a thick-walled flask closed by a cork bearing a thermometer 
reaching almost to the bottom, treat 50 grammes of pure (in vac- 
uum distilled), cooled acetacetic ester with 8.5 grammes of pure 
aldehyde distilled just before the experiment. The flask is cooled 
to — 10-15 in a freezing mixture of ice and salt. To the Yeac- 
tion-mixture is then added a few drops of diethyl amine from a 
small medicine " dropper." In rriost cases no elevation of tem- 
perature takes- place at first. Since it is very difficult to obtain 
acetacetic ester and aldehyde absolutely free from acids, the first 
portions of the amine are neutralised by the acids present, and are 
thus not available for the main reaction. The addition of the 
amine is continued slowly until at a certain point an elevation of a 
few degrees in the temperature is observed. Normally this should 
occur on the addition of the first ten drops. When this takes 
place, the liquid, clear at first, becomes turbid. From this point, 
during the gradual addition of a further portion of ten drops of the 
base, the temperature is slowly allowed to rise to o°. The addi- 
tion of the base in drops is continued, gradually and with frequent 
shaking, until, collectively, 60 drops =1.5 grammes have been 
used. The length of the operation is about an hour. After the 
reaction-mixture has stood a further quarter hour, it is removed 
from the freezing mixture and allowed to come to the room tem- 
perature. If, in consequence of a secondary reaction, the temper- 

1 A. 281, 25. 



TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 1 77 

ature should go up to 20 , the flask is cooled off a short time in 
ice water. The reaction-product is a viscous, bright yellow liquid 
in which numerous drops of water are suspended. It is allowed 
to stand undisturbed until it solidifies to a crystalline mass, which 
generally requires from two to three days. 

A small specimen is pressed out on a porous plate and recrystal- 
lised from diluted alcohol. Colourless needles are thus obtained 
which melt at 79-80 . 

The solidification of the crude product may be hastened by 
seeding it, after one day's standing, with crystals obtained in a 
previous preparation. This is best done on the upper portion 
of the flask, which is only moistened by the liquid. 

2. DIMETHYLCYCLOHEXENONE 

The crude product liquefied by heating in a water-bath is poured 
into a mixture of 100 grammes of water and 400 grammes of con- 
centrated sulphuric acid contained in a round litre flask provided 
with a long reflux condenser. The reaction-mixture is heated to 
lively boiling on a wire gauze ; a few pieces of unglazed porcelain 
are placed in the flask to insure a regular ebullition. 

After about seven hours' heating (the experiment should be 
commenced in the morning of a working-day), the reflux con- 
denser is replaced by an ordinary condenser, and steam is passed 
into the mixture until the distillate measures about 100 c.c. The 
flask is heated by a free flame up to the boiling-point of its con- 
tents. The distillate is preserved in a well-closed vessel. 

On the second day the mixture is again heated for seven hours 
(with a reflux condenser, new porcelain scraps in the flask), and 
then 100 c.c. are again distilled off with steam. This is repeated 
on the third day, and finally steam is passed into the mixture until 
from a test portion of the distillate saturated with solid potash no 
oil, or only a minute quantity, separates out. The three distillates 
in which the reaction-product is for the most part dissolved are 
now united. Solid potash is added until it is no longer dissolved. 

For the success of the salting out, one must use anhydrous potash 



178 SPECIAL PART 

as pure as possible. From the potash solution a brownish red oily 
layer separates out : it consists of dimethylcyclohexenone and 
alcohol. It is separated from the water solution in a dropping 
funnel, and the alcohol is distilled off by the aid of a Hempel tube 
10 cm. long filled with glass beads. The residue is dried over 
fused Glauber's salt and distilled from an ordinary fractionating 
flask. The portion going over between 200-2 15 is collected 
separately. Boiling-point of the pure compound, 211 . Yield, 
15-20 grammes. 

3. s-XYLENOL 

A mixture, cooled by ice water, of 10 grammes of the ketone 
dissolved in 20 grammes of glacial acetic acid (the acid must not 
be allowed to solidify) is treated gradually with a mixture of 13 
grammes of bromine and 10 grammes of glacial acetic acid from 
a dropping funnel. The reaction-mixture is then allowed to stand, 
under the hood, at least half a day, or better over night, at the 
room temperature. Hydrobromic acid is evolved copiously. The 
mixture is heated, with frequent shaking, about an hour on a water- 
bath to about 50 , the temperature is then increased until the 
water boils, and the heating is continued until there is only a 
slight evolution of hydrobromic acid. It is heated finally, using 
an air condenser, on a wire gauze, to incipient ebullition of the 
acetic acid, until the evolution of hydrobromic acid almost entirely 
ceases. After cooling, it is poured carefully into a cooled solution 
of 75 grammes of caustic potash in 150 grammes of water, upon 
which only a small quantity of an oil should separate out. The 
by-products insoluble in the alkaline solution are extracted with a 
sufficient quantity of ether, the alkaline solution is saturated with 
carbon dioxide, and the s-xylenol liberated is distilled over in the 
presence of carbon dioxide with steam (use a three-hole cork). 
The end of the distillation may be readily determined. So long 
as the xylenol is coming over, a test of the distillate by adding a 
few drops of bromine will show a precipitate of tribromxylenol. 

If the distillate be allowed to stand in a cool place over night, 



TRANSITION FROM ALIPHATIC TO AROMATIC SERIES I 79 

the larger portion of the xylenol will crystallise out. In order to 
obtain the portion remaining dissolved, the crystals are filtered off, 
and the filtrate saturated with solid salt and extracted with ether. 
Melting-point of s-xylenol, 64 . Boiling-point, 2 20-2 2 1°. Yield, 
5-6 grammes. 

A better characterisation of this phenol is obtained by covering 
a few drops of it in a test-tube with 5 c.c. of water and then adding 
bromine drop by drop until the reddish brown colour of the latter 
does not disappear. The excess of bromine is removed by the 
addition of a solution of sulphur dioxide. The precipitate is 
recrystallised from alcohol. There are thus obtained colourless 
needles of tribromxylenol, which melt at 165 . 

Aldehydes unite, with the elimination of water, with compounds 
containing the group CH 2 between two negative radicals (acetacetic 
ester, malonic ester, acetylacetone, and others), in two ways. 1. Equal 
molecules unite in accordance with the following equation : 



HL + O 



HC.R 



X 

I 
H 2 + C = CH.R 

I 
Y 



Example 



CH 3 

I 
CO 



H 2 + 



CH 3 

I 
CO 

I 

HC.CH3 = H 2 + C = CH .CH, 

I 



Ethylideneacetacetic ester 

i. The reaction may take place between one molecule of the alde- 
hyde and two molecules of the other compound : 



X 



R 



X 



X 



R 



X 



CH |h[ + CH|0 + h! HC = H 2 + CH - CH - CH 



i8o 



SPECIAL PART 



Example, carried out in practice: 
CH fl 
CH, 



CH 3 ^-^3 

CO CH Q CO 



CH|Ti] + CH|0 + H|CH=:H 2 

I I 

COOC 2 H 5 



CH 3 
CO 

I 

CH 

I 



CH 3 
CH 



CH 3 

CO 

I 
CH 

I 



Ethylidenebisacetacetic ester. 



For bringing about the first reaction the following-named substances 
may be used as condensation agents : hydrochloric acid, acetic anhy- 
dride, as well as primary and secondary amines (ethyl amine, diethyl 
amine, piperidine, and others). For the second reaction the bases 
mentioned may be used. A small quantity of one of these may pro- 
duce large quantities of the condensation product : this is a case of a 
so-called continuous reaction. It is probable that the amine reacts 
first with the aldehyde, water being eliminated : 1 



R.CH 



Q + H 2 | N.R 1 = R.CH = N.R 1 + H 2 

prim, amine 



/NR" 
NR" / 

iNK = RCH +H 2 

NR " \NR" * 

(R" = a bivalent radical or two univalent radicals.) 

In the example above : 

, , /N(C 2 H 5 ) 2 

CHj.CHO + 2H N(C 2 H 5 ) 9 = CH 3 .CH< -f- H 2 
X N(C 2 H 5 ) 2 



The aldehyde derivative thus formed then acts upon the second com- 
pound with the regeneration of the amine : 



X 



R.CH = NR 1 + H 2 C = R 1 NH 2 + C=CH.R 
Y Y 



1 B. 31, 738. 



TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 1 8 1 

X X R X 

I III 

CH = 2 HNR n + CH - CH - CH 

I i I 

Y Y Y 



X 


R 

1 




chIH 

1 


1 
+ CH + 


H 


Y 


N|R n NR U | 



In the above example : 

CH 3 R 

CO CH 



I 

CHH + N(C 2 H 5 ) 2 



N(C 2 H 5 ), 



CH. 

I 
CO 

I 

HCH 

I 



CH. 



CH. 



CO 

I 



CHg CO 

I I 



= 2 NH(C 2 H 5 ) 2 + CH - CH - CH 

COOC 2 H 5 COOC 2 H 5 

The amine thus regenerated carries over anew the aldehyde residue to 
the acetacetic ester, and so on. 

2. Of the compounds which can be obtained by reaction (2), of 
especial interest are those which, like the ethylidenebisacetacetic ester 
prepared above, contain two carbonyl groups (1.5 diketones) and in 
addition a methyl group. If such compounds are treated with those 
substances which have the power to eliminate water (alkalies or acids), 
six-membered carbon rings are formed as follows : 



R.CH 



X . CH - CO 

/ 



X - CH - CO 



H. 



X.CH-C O 



CH =H + R.CH 
\ 



CHc 



CH 



X - CH - C - CH, 



In the above example : 
C,H,OOC - CH - CO 



C 2 H 5 OOC 



C 2 H.OOC - CH 



CH 



H,0 + 



CH 3 



C 2 H 5 OOC 



- CH - CO 
/ \ 

:h ch 

\ // 

-CH -C-CH. 



1 82 SPECIAL PART 

Beside this ring closing, a second reaction takes place in the experiment 
made above. The sulphuric acid saponifies the primarily formed acid- 
ester, with the elimination of carbonic acid : 



HO 



C 2 H 



H 

I-O 
\ 

CH = 2 C0 2 + 2 C 2 H,OH + CH 3 -CH 



OOC.CH-CO CH 2 -CO 



C 2 H 5 
HO 



OOC.CH-C-CHo CH 2 -C-CH S 

H Dimethylcyclohexenone 



This ring closing with 1.5 diketones is capable of many modifications. 
By using formaldehyde, acetaldehyde, proprionaldehyde, benzaldehyde, 
etc., R = H, CH 3 , C 2 H 5 , C 6 H 5 , etc. By using acetaceticester, acetylace- 
tone, benzoylacetone, etc., X = COOC 2 H ; ,, CH 3 C6, C 6 H 5 CO, etc. 

The many-sidedness of the reaction is materially increased by starting 
with the unsymmetrical 1.5 diketone, e.g.: 



I I 

CO R CO 

I I I 

CH - CH - CH 



COOCH, 



The nature of the reaction requires, however, that one of the two car- 
bonyl groups must be connected with a methyl group, otherwise the 
elimination of water cannot take place. The compounds so obtained 
are all derivatives of the mother substance : 



/ \ 

CH 9 CH 

\ S 

CH 2 - CH 

which is called cyclohexenone, and which may be considered as the 
keto-derivative of tetrahydrobenzene 



CH 2 - 


-CH 


/ 


\ 


CH 2 


CH 


\ 


// 



CH, - CH 



TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 1 83 

This, therefore, is a transition from the aliphatic to the (hydro) aromatic 
series. 

This primarily obtained compound may by different reactions be 
converted into other hydroaromatic and aromatic substances. If, e.g., 
the dimethylcyclohexenone be reduced, the ketone group is converted 
into the secondary alcohol group, at the same time the double union is 
severed, and two hydrogen atoms are added on, so that there is obtained 
an alcohol derivative of hexahydro-benzene or -xylene. 

OH 

CH,-CH 

/ - \ 
CH, - CH CH 2 

\ / 

CH 2 - CH - CH 3 . 

Hexahydroxylenol 

If this compound be oxidised, the secondary alcohol group is changed 
to a ketone group, and a keto-derivative of a hexahydroxylene is formed : 

CH, - CO 

/ ~ \ 

CH. - CH CH, 

\ / 

CH 2 - CH - CH 3 

If the hexahydrogen addition alcohols be treated with substances hav- 
ing the power to eliminate water, there is obtained a tetrahydrogen 
addition product of the hydrocarbon, e.g. : 

CH, - CH 

/ " % 
CH 3 . CH CH = Tetrahydroxylene 

CH, — CH . CHg 

If in compounds like hexahydroxylenol, the hydroxyl be replaced by 
iodine, and the resulting iodide reduced, there is obtained a hexahy- 
drogen addition product of the hydrocarbon, e.g. : 

CH, - CH, 

/ " V 
CH, . CH CH, = Hexahydroxylene 

\ / 

CH,-CH.CH, 

It is thus evident that the syntheses of a great variety of hydroaromatic 
compounds are possible. 



1 84 SPECIAL PART 

3. By these reactions the compounds of the pure aromatic series 
may be reached. If bromine be allowed to act on the primarily arising 
ring compound, as has been done practically, the double union is broken 
up by the addition of two atoms of bromine : 



CH 2 -CO CH 2 - 


-CO 


/ \ / 


\ 


CH 3 . CH CH + Br 9 = CH 3 . CH 


CHBr 


\ // ■ " \ 


/ 


CH2 — C — CH 3 CH 2 - 


- CBr - CH 



These dibromides are very unstable, and even in the cold give off two 
molecules of hydrobromic acid : 

CH„ - CO 

^— ^ 

CH 3 .C H FMCH = 2 HBr + CH 3 - C CH 

\ 7 % // 

CH - C - CH, CH - C - CH, 

II 
|H Br I 



Finally, this unstable keto-form (CH 2 - CO) changes itself into the 
stable enol-form (CH = C.OH), and the s-xylenol is obtained. 

OH 

I 
CH = C 

/ \ 

CH 3 .C CH 

CH-C 

I 
CH 3 

For further information concerning the transition from aliphatic 
to aromatic or hydroaromatic compounds, compare Bernthsen, VII Ed., 
p. 336; Richter, VII Ed., Vol. II, pp. 4, 5, and 24; Krafft, II Ed., 
p. 440; Meyer-Jacobson, II Vol., p. 79. 



AROMATIC SERIES 1 85 



II. AROMATIC SERIES 

1. REACTION: NITRATION OF A HYDROCARBON 

Examples : Nitrobenzene and Dinitrobenzene l 

Nitrobenzene 

To 150 grammes of concentrated sulphuric acid contained in a 
£-litre flask, add gradually, and with frequent shaking, 100 grammes 
of concentrated nitric acid (sp. gr. 1.4). After cooling the mix- 
ture to the room temperature, by immersion in water, gradually 
add 50 grammes of benzene, with frequent shaking. If the tem- 
perature should rise above 50-60 , the operation is interrupted, 
and the flask immersed in water for a short time. When all of the 
benzene has been added, a vertical air condenser is attached to 
the flask ; it is then heated in a water-bath for an hour at 6o° 
(thermometer in the water) ; during the heating the flask is fre- 
quently shaken. After cooling, the lower layer, consisting of sul- 
phuric and nitric acids, is separated from the upper layer of 
nitrobenzene in a separating funnel. The nitrobenzene is then 
agitated in the funnel several times with water : it must be borne 
in mind that the nitrobenzene now forms the lower layer. After 
being washed, it is placed in a dry flask, and warmed on a water- 
bath with calcium chloride until the liquid, milky at first, becomes 
clear. It is finally purified by distillation from a fractionating 
flask provided with a long air condenser. Boiling-point, 206-207 . 
Yield, 60-70 grammes. 

Dinitrobenzene 

To a mixture of 25 grammes of concentrated sulphuric acid and 
15 grammes of fuming nitric acid, 10 grammes of nitrobenzene are 
1 A. 9, 47; 12, 305. Ostwald's Klassiker der exacten Wissenschaften Nr. 98. 



1 86 SPECIAL PART 

gradually added (hood) ; the reaction-mixture is then heated for 
half an hour on a water- bath, with frequent shaking • after cooling 
somewhat, it is poured, with stirring, into cold water. The dinitro- 
benzene which solidifies is filtered off, washed with water, pressed 
out on a porous plate, and recrystallised from alcohol. Melting- 
point, 90 . Yield, 10-12 grammes. 

The property of yielding nitro-derivatives, when treated with nitric 
acid, is a characteristic of aromatic compounds. According to the 
conditions under which the nitration is carried out, one or more nitro- 
groups can be introduced at the same time. The above reactions take 
place in accordance with the following equations : 

C C H 6 + N0 2 . OH = C 6 H- . N0 2 + H 2 0, 

C 6 H, . N0 2 + N0 2 . OH = C fi H 4 . (N0 2 ) 2 + H 2 0. 

If a saturated aliphatic residue is present in an aromatic compound, 
the nitration under the above conditions always affects the benzene 
ring, and not the side-chain. Since the benzene carbon atoms are in 
combination with only one hydrogen atom, the nitro-compounds ob- 
tained on nitration are tertiary ; they therefore do not have the power 
to form salts, nitrolic acids, or pseudo-nitroles, like the primary and 
secondary nitro-compounds. 

Recently the nitro-group has been introduced directly into the side- 
chain. 1 If, e.g., toluene or ethyl benzene be heated with weak nitric 
acid (sp. gr. 1.076) in a bomb up to about ioo°, phenylnitromethane, 
C 6 H 5 . CH 2 . N0 2 , or phenylnitroethane, C 6 H S . CH . N0 2 . CH 3 is ob- 
tained. 

Not only can the mother substances, the aromatic hydrocarbons, but 
all their derivatives, as phenols, amines, aldehydes, acids, etc., undergo 
similar reactions. But the nitration does not take place in every case 
with the same ease. In each case, therefore, the most favourable con- 
ditions for the experiment must be determined. If a compound is very 
easily nitrated, the nitration may be effected, according to the condi- 
tions, by nitric acid diluted with water, or the substance may be dis- 
solved in a solvent which is not attacked by nitric acid ; glacial acetic 
acid is frequently used for this purpose, and then treated with nitric 
acid. The reverse process may also be employed, i.e. the substance is 
added to a mixture of nitric acid and water, or nitric acid and glacial 
acetic acid. If a substance is moderately difficult to nitrate, it is added 



1 B. 27. Ref. 194 and 198. 



AROMATIC SERIES 1 87 

to concentrated or fuming nitric acid. If the nitration is difficult, the 
elimination of water is facilitated by the addition of concentrated sul- 
phuric acid to ordinary or fuming nitric acid. In the nitration, the 
substance may either be added to the mixture of nitric acid and sulphuric 
acid, or the nitric acid is added to the substance dissolved in concen- 
trated sulphuric acid. In working with sulphuric acid solutions, at times 
either potassium nitrate or sodium nitrate may be used instead of nitric 
acid. The three nitration methods just described may be still further 
modified in two ways: (1) the temperature may be varied; (2) the 
quantity of nitric acid may be varied. The nitration can be effected in 
a freezing mixture, in ice, or in water, by gentle heating, or finally, at 
the boiling temperature. Further, the theoretical amount of nitric acid, 
or an excess, may be used. In order to determine which of these nu- 
merous modifications will give the best results, preliminary experiments 
on a small scale must be made. Since the nitro-compounds are gener- 
ally insoluble in water, or difficultly soluble, they can be separated from 
the nitrating mixture by diluting it with water, or in many cases better, 
with a solution of common salt. 

The chemical character of a substance is not changed in kind, but in 
degree, by the introduction of a nitro-group. Thus, the nitro-derivatives 
of the hydrocarbons are indifferent compounds like the hydrocarbons. 
If a nitro-group is introduced into a compound of an acid nature like 
phenol, it becomes more strongly acid, e.g. the nitro-phenols are more 
strongly acid than phenol. When a nitro-group is introduced in a basic 
compound, the resulting substance is less basic ; e.g. nitro-aniline is less 
basic than aniline. 

The great importance of the nitro-compounds is due to their behav- 
iour on reduction ; this will be considered under the next preparations. 

Concerning the introduction of the nitro-group, the following laws 
are of general application. 

The introduction of one nitro-group in the benzene molecule can, 
obviously, only result in the formation of one mononitrobenzene. If 
an alkyl radical is present in the benzene molecule, the nitro-groups 
enter the ortho- and para- but not the meta-position to the radical. 
On nitrating toluene, eg., there are formed : 

CH, CH, 



I— NO., , 

- and 



l 

N0 2 



1 88 SPECIAL PART 

The nitro-groups seek the same position when a benzene-hydrogen 
atom has been substituted by hydroxyl. Thus, e.g., phenol gives on 
nitration a mixture of o- and p-nitrophenol. On the other hand, if a 
compound contains an aldehyde-, carboxyl-, or cyanogen-group, on ni- 
tration the nitro-group goes in the meta-position to this. Benzaldehyde, 
benzoic acid, and benzonitrile give on nitration respectively : 

CHO CO. OH CN 

/\ /\ /\ 

^/'no, \J no > \J n ° 2 

If a compound already contains a nitro-group, a second one will take 
the meta-position to this. Thus, on nitrating nitrobenzene, m-dinitro- 
benzene is formed. O-nitrotoluene or o-nitrophenol yield on nitrating : 





respectively. 

From m-nitrobenzoic acid the following dinitrobenzoic acid is formed : 

CO. OH 

N0 2 !^ 

The nitro-compounds are in part liquids, in part solids ; in case 
these latter distil without decomposition, they possess a higher boiling- 
point than the mother substance. 

2. REACTION: REDUCTION OF A NITRO-COMPOUND TO AN AMINE 

Examples: (i) Aniline from Nitrobenzene * 

(2) Nitroaniline from Dinitrobenzene 

A mixture of 90 grammes of granulated tin and 50 grammes 
of nitrobenzene is placed in a i^-litre round flask. To this are 
gradually added 200 grammes of concentrated hydrochloric acid 

1 A. 44, 283. 



AROMATIC SERIES 1 89 

in the following manner : At first only about one-tenth of the 
acid is added ; an air condenser, not too narrow, is then attached 
to the flask and the mixture well shaken. After a short time it 
becomes warm, and finally an active ebullition takes place. As 
soon as this happens, the flask is immersed in cold water until the 
reaction has moderated. The second tenth of the acid is then 
added, and the above operation repeated. After one half of the 
acid has been used, the reaction becomes less violent, and the 
second half may be added in larger portions. In order to effect 
the reduction of the nitrobenzene completely, the mixture is 
finally heated one hour on the water-bath. To separate the free 
aniline, the warm solution is treated with 100 c.c. of water, then a 
solution of 150 grammes of caustic soda in 200 grammes of water 
is gradually added. If the action of the caustic soda causes the 
liquid to boil, the flask is cooled by water for a short time, before 
a further addition of caustic soda. When all of the solution has 
been added, a long condenser is attached to the flask, and steam 
is passed into the hot liquid, upon which aniline, as a colourless 
oil, and water pass over, the aniline collecting under the water. 
As soon as the distillate no longer appears milky, and becomes 
clear, the receiver is changed and about 300 c.c. more of the 
liquid distilled over. The distillates are mixed, treated with 25 
grammes of finely powdered sodium chloride for every 100 c.c. 
of the liquid, shaken until all the salt is dissolved, and the aniline 
extracted with ether. After the ethereal solution has been dried 
by treating it with a few pieces of solid potassium hydroxide, 
the ether is evaporated and the aniline subjected to distillation. 
Boiling-point, 182 . Yield, 90-100% of the theory. If the 
circumstances are such as not to permit the experiment to be 
completed without interruption, it is so arranged that the neu- 
tralisation with sodium hydroxide, and the distillation with steam 
immediately following, may take place within a short time, so -that 
the heat of neutralisation may be utilised. 

To the nitro-compounds of the aromatic series, as well as those of 
the aliphatic series, belongs the property of being converted into primary 

For the reduction of every nitro-group, 



190 SPECIAL PART 

six atoms of hydrogen are necessary, and the following equation is the 
general expression of the reaction : 

X . N0 2 + 3 H 2 = X . NH 2 + 2 H 2 0. 

For the reduction of nitro-compounds on the small scale in the 
laboratory, it is most convenient to use, as the reducing agent, granu- 
lated tin and hydrochloric acid, or stannous chloride and hydrochloric 
acid: 

(1)2 C 6 H 5 . N0 2 + 3 Sn + 12 HC1 = 2 C G H 5 . NH 2 + 3 SnCl 4 + 4 H 2 0, 
(2) C 6 H 5 . N0 2 + 3 SnCl 2 + 6 HC1 = C fi H 5 . NH 2 + 3 SnCl 4 + 2 H 2 0. 

To 1 molecule of a mononitro-compound, i\ atoms of tin, or 3 mole- 
cules of stannous chloride, are therefore used. In calculating the amount 
of the latter necessary for a reaction, it is to be remembered that the salt 
crystallises with two molecules of water (SnCl 2 + 2 H 2 0). If the re- 
duction is to be effected by metallic tin, double the above quantity is 
frequently used, i.e. to 1 nitro-group, 3 atoms of tin. In this case, the 
tin is not converted into stannic chloride, but into stannous chloride : 

C 6 H 5 . N0 2 + 3 Sn + 6 HC1 = C 6 H 5 . NH 2 + 3 SnCl 2 + 2 H 2 

Since, in the cases mentioned, hydrochloric acid is always present 
in excess, and the amines unite with it to form soluble salts, the end 
of the operation occurs when no more of the insoluble nitro-compound 
is present, and the reaction-mixture dissolves clear in water. In order 
to get the free amine from the acid mixture, various methods may be 
employed. If, as in the above example, the amine is volatile with 
steam, and insoluble in alkali, then the acid solution is treated with 
caustic potash, or caustic soda, until the oxide of tin which separates 
out at first is redissolved in the excess of alkali ; the liberated amine 
is driven over with steam. Further, volatile or non-volatile amines 
can be extracted from an alkaline solution by a proper solvent, like 
ether. But this process is often troublesome, since the alkaline tin 
solution forms an emulsion with ether, which subsides with great diffi- 
culty. If the free amine is solid, it may be obtained by filtering off the 
alkaline liquid. In many cases, where a non-volatile amine is under 
examination, it is advisable to precipitate the tin before liberating the 
amine. This is done by diluting the acid solution with much water, 
heating on the water-bath, and as soon as the liquid has reached the 
temperature of the bath, hydrogen sulphide is passed into it. The tin 
is precipitated as stannous or stannic sulphide ; this is separated from 



AROMATIC SERIES 191 

the amine hydrochloride by filtering. Since tin, in the presence of a 
large excess of hydrochloric acid, is precipitated only with difficulty by 
hydrogen sulphide, it is frequently necessary to drive off the excess 
of the acid before treating with hydrogen sulphide. This is done by 
evaporating to dryness on the water-bath. 

After the tin sulphide has been filtered off, a portion of the filtrate 
is tested with hydrogen sulphide for tin ; if it should be present, the 
whole filtrate is evaporated on the water-bath, as completely as possible, 
to remove the hydrochloric acid, then diluted with water, and hydrogen 
sulphide is again passed into it. At times, the amine forms with 
hydrochloric acid, a difficultly soluble salt, or the amine hydrochloride 
combines with the tin chloride to form a difficultly soluble double salt. 
In this case, the isolation of the amine may be facilitated by filtering 
it off, washing with hydrochloric acid, and pressing out on a porous 
plate, if necessary. If one is dealing with amines, which, like amido- 
acids, possess an acid character, obviously, these cannot be separated 
by the use of an alkali, as in the above example. In a case of this 
kind, the tin is always removed first, the acid solution evaporated to 
dryness, and the amido-compound is now liberated by the addition 
of sodium acetate. With amido-phenols, sodium hydrogen carbonate, 
sodium carbonate, or sodium sulphite may be used to decompose the 
hydrochloric acid salt. 

In the laboratory, other metals, like iron, zinc, etc., in connection 
with an acid, are only rarely used in the place of tin or stannous 
chloride, for the reduction of nitro-compounds. On the large scale, 
iron, owing to its cheapness, is used in the preparation of bases like 
aniline, toluidine, a-naphthyl amine, etc., from the corresponding nitro- 
compounds. By the use of iron and hydrochloric acid, the reduction 
should theoretically take place in accordance with the following equa- 
tion : 

C 6 H 5 .N0 2 + 3 Fe + 6HC1 = 3 FeCl 2 + 2 H 2 + C 6 H 5 .NH 2 . 

As a matter of fact, on the large scale, much less hydrochloric acid 
(only ^0) is used than that required by the above equation. In the 
presence of ferrous chloride, the nitro-compound is reduced by the iron 
without the action of hydrochloric acid, according to the equation : 

C 6 H 5 . NO, + 2 Fe + 4 H 2 = C 6 H 5 . NH 2 + 2 Fe(OH) 3 

For the neutralisation of the hydrochloric acid, a small quantity of 
which is always used on the large scale, slaked lime is employed in 
preference to the more costly alkalies. 



192 SPECIAL PART 

The complete reduction of nitro-compounds containing several nitro- 
groups is conducted in the same way as for mononitro-compounds. 
If it is desired to reduce but one or two of several nitro-groups, it 
cannot be done by adding just the calculated amount of the reducing 
agent ; for cases of this kind, special methods are necessary. For this 
purpose, hydrogen sulphide in the presence of ammonia or ammonium 
sulphide is often used for the reduction : 

HoS = Ho -j" S 

The compound to be reduced is dissolved in water or alcohol, accord- 
ing to circumstances, treated with ammonia, heated, and hydrogen 
sulphide passed into it ; or it is heated in a water or alcohol solution 
with a previously prepared water or alcohol solution of ammonium 
sulphide. In this way, e.g., dinitrohydrocarbons may be converted 
into nitro-amines. A second method, which may be generally used for 
the reduction, step by step, of compounds containing several nitro-groups, 
is this : An alcoholic solution of the theoretical amount of stannous 
chloride saturated with hydrochloric acid is gradually allowed to flow 
into an alcoholic solution of the substance to be reduced, which is well 
cooled, and constantly shaken. (B. 19, 2161.) 

Experiment : l The recrystallised dinitrobenzene is dissolved in 
alcohol (4 grammes alcohol to 1 gramme dinitrobenzene), in a 
flask, the solution is quickly cooled down, upon which a portion 
of the dinitrobenzene separates out ; it is then treated with 0.8 
gramme of concentrated ammonia for 1 gramme dinitrobenzene 
(the ordinary dilute solution of ammonia employed as a reagent 
must not be used). After the flask and its contents have been 
tared, the mixture is saturated with hydrogen sulphide at the 
ordinary temperature; the current of hydrogen sulphide is then 
shut off, and the flask, provided with a reflux condenser, is heated 
for about half an hour on a water-bath. It is then allowed to cool 
to the ordinary temperature, and hydrogen sulphide again passed 
into it to saturation, etc. This operation is repeated until there 
is an increase of 0.6 gramme in weight for every gramme of dini- 
trobenzene used. If in consequence of insufficient cooling the 
required increase in weight does not take place, hydrogen sulphide 

1 A. 176 M . 



AROMATIC SERIES 1 93 

is again passed into the mixture. It is then diluted with water, 
the precipitate filtered off, washed with water, and extracted 
several times by warming with dilute hydrochloric acid. From 
the acid filtrate, the nitro-aniline is set free by neutralising with 
ammonium hydroxide ; it is recrystallised from water. Melting- 
point, 1 1 4 . Yield, 70-80% of the theory. 

/NO, /N0 2 

C 6 H 4 < +3H 2 S=C 6 H/ +2H.0 + 3S 

\N0 2 \NH 2 

Special methods are necessary for the reduction of nitro-compounds 
containing groups capable of being acted upon by hydrogen, e.g., an 
aldehyde-group, an unsaturated side-chain, etc. In cases of this kind, 
ferrous hydroxide is frequently used : 

2 Fe(OH) 2 + 2 H 2 = 2 Fe(OH) 3 + H 2 

The reduction is effected by adding to the substance to be reduced, 
in the presence of an alkali (potassium-, sodium-, or barium-hydrox- 
ide), a weighed quantity of ferrous sulphate. By this reaction, o-nitro- 
benzaldehyde is reduced to o-amidobenzaldehyde ; o-nitrocinnamic acid 
to o-amidocinnamic acid. 

As a perfectly neutral reducing agent, which appears to be well 
adapted for a great variety of reduction reactions, aluminium amalgam 1 
is recommended. It is made by treating aluminium filings or shavings, 
which have been slightly acted on by caustic soda, with a solution of 
mercuric chloride. It reacts with water in accordance with this equation : 

Al + 3 HOH = Al(OH) 3 + 3 H 

Besides the reducing agents mentioned, there is still a large number 
of others which find only an occasional application in reducing nitro- 
compounds to amines. They will be referred to under the different 
preparations. 

The primary mon-amines are in part colourless liquids, e.g., aniline, 
o-toluidine, xylidine ; or colourless solids like p-toluidine, pseudo- 
cuminidine, the naphthyl amines, etc. They can be distilled without 
decomposition, are volatile with steam, and difficultly soluble in water. 
The di- and poly-amines are for the most part solids, non-volatile with 
steam, and much more readily soluble in water than the mon-amines. 

1 B. 28, 1323. 
o 



194 SPECIAL PART 

The amines possess a basic character, but the basicity is weaker than 
that of the aliphatic amines, in consequence of the negative nature 
of the phenyl group. 

Salts: C 6 H 5 .NH 2 .HC1 . . . . Aniline hydrochloride 
C 6 H 5 .NH 2 .HN0 3 . . . Aniline nitrate 
(C 6 H 5 .NH 2 ) 2 .H 2 S0 4 . . Aniline sulphate 

Like ammonia, the amines unite with calcium chloride to form double 
compounds ; for this reason they must not be dried with this substance 
(see page 47). 

The primary mon-amines find numerous applications in the labora- 
tory, as well as on the large scale, in consequence of their great activity. 
Frequent reference will be made to the subject in the following pages. 

With the aniline prepared above, the following experiments are 
made: 

(1) Add 3 drops of aniline to 10 c.c. of water in a test-tube, 
and shake the mixture. The aniline dissolves. At moderate tem- 
peratures, 1 part of aniline dissolves in about 30 parts of water. 

(2) Dilute 1 c.c. of this aniline solution with 10 c.c. of water, 
and add a small quantity of a filtered water solution of bleach- 
ing powder. A violet colouration takes place ; by this reaction 
(Runge's), the most minute quantity of free aniline may be de- 
tected. If in this experiment the solution should not remain clear, 
but a dirty violet precipitate separate out, a too concentrated solu- 
tion has been used ; the aniline water is diluted further, and the 
experiment repeated. If a salt of aniline is to be tested, it is dis- 
solved in water, treated with alkali, the free aniline extracted with 
ether, this latter evaporated, and the residue dissolved in water. 
Then proceed exactly as just directed. 

This reaction may also be used to detect small quantities of 
benzene or nitrobenzene. In a test-tube mix 5 drops of concen- 
trated sulphuric acid with 5 drops of concentrated nitric acid, 
then add 1 drop of benzene, shake, and warm gently by passing 
the tube through a flame several times. Then add 5 c.c. of 
water, and extract the nitrobenzene with a little ether ; the ether 
layer is removed with a capillary pipette, and the ether evapo- 
rated. The residue is treated with 1 c.c. of concentrated hydro- 



AROMATIC SERIES 1 95 

chloric acid, and to this is added a piece of zinc the size of a 
lentil, to effect the reduction. When the zinc is dissolved, the 
mixture is diluted with water, and made strongly alkaline, until 
the hydroxide of zinc precipitated at first is redissolved ; the ani- 
line is then extracted with a little ether. Then proceed as just 
described. 

If it is desired to determine whether a given compound is 
nitrobenzene, it is at once reduced with zinc and hydrochloric 
acid. 

(3) In a small porcelain dish place 5 drops of concentrated 
sulphuric acid, and with a glass rod add 1 drop of aniline. The 
aniline sulphate thus formed solidifies for the most part on the 
rod ; remove it by rubbing it against the walls of the dish. Then 
add 4 drops of an aqueous solution of potassium dichromate, and 
mix the liquid by revolving the dish. After a short time the liquid 
assumes a beautiful blue colour. If the reaction does not take 
place, add 2 more drops of the dichromate, or heat a moment 
over a small flame. 

(4) Isonitrile Reaction : Heat a piece of caustic potash the 
size of a bean with 5 c.c. of alcohol, pour off the solution from the 
undissolved residue into another test-tube ; the warm solution is 
treated with 1 drop of aniline and 4 drops of chloroform. A re- 
action takes place immediately, or on gentle warming; this is 
recognised not only by the separation of potassium chloride, but 
by a most highly characteristic, disagreeable odour. The odour 
becomes more pronounced on pouring off the liquid and adding 
some cold water to the tube. If the vapours of the isonitrile are 
inhaled through the mouth, a peculiar sweet taste is noticed in 
the throat. 

The reaction must be carried out under a hood with a good 
draught. 

While the two colour reactions with bleaching powder and chromic 
acid are used especially for the recognition of aniline, the isonitrile 
reaction will show the presence of any primary amine of the aliphatic 
or aromatic series. The reaction takes place in accordance with the 
following equation : 

C 6 H 5 . NH 2 + CHClo = C 6 H 5 . NC + 3 HC1 



196 SPECIAL PART 

For the elimination of hydrochloric acid, caustic potash is added. 
Since all isonitriles or carbylamines possess a characteristic odour, on 
the one hand the smallest quantity of a primary base may be detected 
by this reaction, and on the other a base may be shown to be primary. 
Secondary and tertiary bases do not give the reaction. 

In the isonitriles it is very probable that the carbon atom combined 
with the nitrogen atom is only bivalent: C 6 H 5 . N=C::::. The iso- 
nitriles are isomeric with the acid-nitriles, e.g., C 6 H 5 .C=N, benzo- 
nitrile. While the nitriles on saponification give acids, the isonitriles 
decompose into a primary amine and formic acid : 

C 6 H 5 . CN + 2 H 2 = C 6 H 3 . CO . OH + NH 3 

C 6 H 5 . NC + 2 H 2 = C 6 H 5 . NH 2 + H . CO . OH 



3. REACTION : (a) REDUCTION OF A NITRO-COMPOUND TO A HYDROX- 
YLAMINE DERIVATIVE. (6) OXIDATION OF A HYDROXYLAMINE 
DERIVATIVE TO A NITROSO-COMPOUND 

Examples : (a) Phenylhydroxylamine from Nitrobenzene * 
(b) Nitrosobenzene from Phenylhydroxylamine 

(a) Phenylhydroxylamine: In a thick-walled J-litre flask treat 
a solution of 5 grammes of ammonium chloride in 160 c.c. of 
water with 10 grammes freshly distilled nitrobenzene. In the 
course of an hour add gradually in small portions, with good 
shaking, 15 grammes of zinc dust; during this operation the tem- 
perature is held constantly between 14 and 16 (thermometer in 
the liquid) by immersing the flask from time to time in ice water. 
After the reaction is complete, the mixture is frequently shaken 
and allowed to stand for about ten minutes at the same tempera- 
ture ; it is then filtered, using suction and a Buchner funnel, from 
the zinc oxide ; the filtrate (solution I) is poured into a beaker, 
and the zinc oxide deposit on the funnel is washed with 200 c.c. 
of water at 40 ; before the water is poured on the residue, the 
suction is disconnected from the funnel, and is only attached after 



1 Modified in accordance with the kind suggestion of Professor Bamberger, 
Zurich. 



AROMATIC SERIES 197 

there has been time enough for the phenylhydroxylamine to be 
dissolved. Use only a gentle suction (solution II). 

The two water solutions are separately cooled in ice water and 
saturated (with stirring) with finely pulverised salt ; for solution 
I, about 45 grammes, and for solution II, about 60 grammes of 
salt will be required. The colourless crystals separating out are 
filtered off with suction, and, without washing, are pressed out on 
a porous plate. Yield, almost quantitative. 

A small test-portion of the crude product is recrystallised from 
benzene. Melting-point, 8i°. The remainder, without further 
purification, is worked up into nitrosobenzene. 

The success of the reaction depends essentially upon the quality 
of the zinc dust used. It is therefore necessary to make a zinc 
dust determination (see p. 356), and then use about 10% more 
than is required by the theory. Zinc dust of 75% is referred to 
above. 

Precautions : In the preparation of phenylhydroxylamine, care 
is taken to prevent it, and particularly a warm solution of it, from 
coming in contact with the skin, since it causes very painful and 
annoying inflammation. Even in pressing it out or pulverising it 
under the hood, care must be taken not to breathe in any of the 
dust, since it causes extraordinarily violent attacks of sneezing. 

(p) Nitrosobenzene : To a solution of 30 grammes of con- 
centrated sulphuric acid in 270 c.c. of water, well cooled by ice 
water, add 4 grammes of freshly prepared and finely pulverised 
phenylhydroxylamine ; the solution is then quickly treated with 
an ice-cold solution of 4.6 grammes of potassium dichromate 
in 200 c.c. of water ; the pure nitrosobenzene separates out imme- 
diately in crystals. 

" On account of the splendid phenomena, steam should be 
passed into the oxidation liquid ; the total quantity of nitroso- 
benzene is carried over in 4-5 minutes. At the beginning of 
the heating the walls and neck of the flask take on a deep 
green colour, and soon the nitrosobenzene sublimes in white, lus- 
trous plates in the bent tube entering the condenser ; a few 
moments later beautiful emerald-green oil drops appear which 



198 SPECIAL PART 

solidify so completely, in the lower part of the condenser, to snow- 
white crystals, that the distillate presents the appearance of a 
faintly green liquid containing only a few minute crystals. The 
crystals of nitrosobenzene are pushed out of the condenser with a 
glass rod, the end being covered with a cotton plug, spread out 
on a porous plate and washed upon the plate with ligroin (boiling- 
point 40-70 ). Melting-point 67.5-68 ." 

(a) The primary amines discussed in the preceding reaction are the 
lowest reduction products of nitro-compounds. Recently two classes of 
compounds have been discovered which appear to be intermediate prod- 
ucts between the nitro-compounds and amines. In order to distinguish 
them from the compounds referred to in the next preparation, they may 
be called " monomolecular intermediate reduction products." 

C 6 H 5 .N0 2 -^C G H 5 .NO~^C c H 5 N< _^C 6 H 5 .NH 2 

M3H 

Nitrobenzene Nitrosobenzene Phenylhydroxylamine Aniline 



Phenylhydroxylamine 1 was obtained simultaneously by Bamberger 
and Wohl by the reduction of nitrobenzene with zinc dust in a neutral 
solution : 

C H 5 NO., + 2 Zn -f H.,0 = C H 5 N< + 2 ZnO 

. X)H 

The presence of certain salts, e.g., calcium or ammonium chloride, pro- 
motes the reaction. Phenylhydroxylamine acts like a base towards acids. 
If it be warmed with mineral acids, it undergoes a noteworthy transfor- 
mation into paraamidophenol : 

/H /NH 2 

C 6 H 5 N< — ^C H/ 

X)H x OH 

This behaviour explains the electrolytic reduction of aromatic nitro- 
compounds. 2 

If a nitro-compound dissolved in concentrated sulphuric acid is 
subjected to electrolytic reduction, not only is the nitro-group reduced 
to the amido-group, but a hydroxyl group enters the para position (to the 
amido-group) if it is vacant. Thus from nitrobenzene p-amidophenol 
is obtained. In accordance with our present knowledge the reaction is 



1 B. 27, 1347, 1432, 1548; 28, 245, 1218. 2 B. 26, 1844, 2810; 27, 1927; 29, 3040. 



AROMATIC SERIES 1 99 

no longer considered remarkable. Phenylhydroxylamine is first formed, 
which immediately undergoes a molecular transformation into the 
amidophenol. 

Phenylhydroxylamine is a strong reducing agent, which reduces 
Fehling's solution and an ammoniacal solution of silver nitrate even 
the cold. With nitrous acid it forms a nitroso-derivative : 

/H .NO 

C G H 5 N< + NOOH = G 6 H 5 N< + H 2 

X)H X)H 

With aldehydes it reacts thus : 



C G H 5 . N< + C 6 H 5 . CHO = C G H 5 . N< >CH . C ( ,H 5 + H O 

X)H XX 

By the oxygen of the air it is oxidised to azoxybenzene ; more energetic 
oxidising agents convert it into nitrosobenzene. 

(b) Nitrosohydrocarbons have not yet been obtained directly by 
reducing the nitro-cornpounds, but when hydroxylamine derivatives are 
oxidised they yield nitroso-compounds : 

/ H 
C G H 5 . N< + O = C 6 H 5 . NO + H 2 

x OH 

The nitrosohydrocarbons in the solid state form colourless crystals, 
but when fused or in solution an emerald-green liquid. They possess a 
characteristic piercing odour which suggests quinone and the mustard 
oils ; they are extremely volatile. On reduction they go over into amines. 
With primary amines they combine to form an azo-compound, e.g., 

C G H 5 . NO + H 2 N . C (i H 5 = C 6 H 5 . N = N . C G H 5 + H 2 

Combined with hydroxylamine they form isodiazo-compounds, e.g., 

C 6 H 5 .NO + NH 2 .OH = C fi H 3 .N = N.OH + H 2 



4. REACTION: REDUCTION OF A NITRO-COMPOUND TO AN AZOXY-, 
AZO-, OR HYDRAZO-COMPOUND 

Examples : Azoxybenzene, Azobenzene, Hydrazobenzene 

(1) Azoxybenzene : x To 200 grammes of methyl alcohol con- 
tained in a 2-litre flask provided with a wide reflux condenser, 
20 grammes of sodium in pieces the size of a bean are gradually 

1 T-P r - 3 6 .93; B - 15. 86 5- 



200 SPECIAL PART 

added ; the flask is not cooled (heat being generated by the re- 
action). Since methyl alcohol frequently contains much water, 
the first portions of the sodium must not be added too rapidly. 
When the metal is dissolved, 30 grammes of nitrobenzene are 
added, and the mixture heated for 3 hours on an actively boiling 
water-bath (reflux condenser). Crystals of sodium formate soon 
begin to separate out ; this often causes a troublesome bumping. 
The greater portion of the methyl alcohol is then distilled off 
(the flask being placed in the water-bath; silk thread). The 
residue is treated with water, and the reaction-mixture poured 
into a beaker. After long standing, especially in a cool place, 
the oil at the bottom solidifies to a bright yellow crystalline mass, 
which is separated from the liquid by decanting the latter ; it is 
washed several times with water and finally pressed out on a 
porous plate. If the azoxybenzene does not solidify, the main 
quantity of the water solution is poured off and the oil treated 
with small pieces of ice. If solidification does not take place 
now, it is due to the presence of nitrobenzene ; this is distilled off 
with steam, and the difficultly volatile residue, after it has cooled, 
is further cooled with ice. From methyl alcohol (use 3 c.c. 
of the alcohol for every gramme of the substance) the azoxy- 
benzene crystallises in bright yellow needles, melting at 36 . 
Yield, 20-22 grammes. 

(2) Azobenzene : x Five grammes of crystallised azoxybenzene, 
dried completely by heating on a water-bath for an hour, are finely 
pulverised and intimately mixed in a mortar with 15 grammes of 
coarse iron filings, which must also be completely dry ; the mixture 
is distilled from a small retort, not tubulated. It is first warmed 
with a small luminous flame kept in constant motion ; the size of 
the flame is increased after some time ; finally the last portions 
are distilled over with a non-luminous flame. If, on heating, a 
sudden but harmless explosion should occur, it is due to the fact 
that the substances were not dry ; the experiment must be re- 
peated. The reddish distillate is collected in a small beaker, and, 
after it has solidified, is washed with hydrochloric acid to remove 

1 A. 12, 311 ; 207, 329. 



AROMATIC SERIES 201 

the aniline, then with water, and pressed out on a porous plate. 
The experiment is repeated a second time with a fresh quantity of 
azoxybenzene ; by working carefully the same retort can be used 
again. The two pressed-out crude products are united. Azoben- 
zene crystallises from ligroin, after a partial evaporation of the 
solvent, in the form of coarse red crystals melting at 68°. 

(3) Hydrazobenzene : 1 Dissolve 5 grammes of azobenzene in 
50 grammes of alcohol (about 95%) in a flask provided with a 
reflux condenser, and treat with a solution of 2 grammes of caustic 
soda in 4 grammes of water. To the boiling solution gradually 
add zinc dust in small portions (best by occasionally removing 
the cork) until the orange -coloured solution becomes colourless : 
about 8 grammes of zinc dust will be necessary. The hot solution 
is then filtered with suction (Buchner funnel) from the excess of 
zinc; 20 c.c. of a water solution of sulphur dioxide and 100 c.c. 
of water are previously placed in the filter-flask. The hydrazo- 
benzene precipitating out of the alcoholic solution is quickly 
filtered, washed with water containing sulphur dioxide, and pressed 
out on a porous plate. By crystallising from ligroin it is obtained 
pure. Melting-point, 12 6°. Yield, 80-90% of the theory. 

Under the influence of suitable reducing agents, nitro-compounds 
undergo a partial reduction in such a way that two molecules enter into 
combination. There are thus obtained first the azoxy-, then the azo-, 
and finally the hydrazo-compound, which in order to distinguish them 
from the compounds obtained in Reaction 3 may be called " dimolecular 
intermediate reduction products." 

C,.H 5 . NO, _Cfi H 5 • N\ C H 5 - N C 6 H S . NH _r H . NHp 

C « H - N °; C 6 H 5 i/ C 6 H 5 J C 6 H 5 i H ^C 6 H 5 .NH 2 

2 Mol. 1 Mol. 1 Mol. 1 Mol. ,» . 

Nitro- — >- Azoxy- — >- Azo- >- Hydrazo- >- A T 

benzene benzene benzene benzene mime 

In order to reduce a nitro-compound to an azoxy-compound, either 
sodium amalgam or alcoholic-caustic potash or caustic soda is used. 
With nitrobenzene, particularly, the reaction takes place most surely 
by dissolving sodium in methyl alcohol as above. The reducing action 
of sodium methylate depends upon the fact that it is oxidised to 

1 Z. 1868, 437. 



202 SPECIAL PART 

sodium formate, two hydrogen atoms of the methyl group being re- 
placed by one atom of oxygen : 

CH 3 . ONa + 2 = H 2 + H . CO . ONa 

In the operation carried out above the reaction is expressed by the 
equation : 



4C 6 H 5 .NO., + 3CH 3 .ONa = 2 >0 + 3 H . CO . ONa + 3 H 2 

C 6 H 5 .N/ 

A few words may be said here concerning the relatively weak reducing 
power of previously prepared alcoholates, in comparison with the 
extremely energetic action of a mixture of undissolved sodium and 
alcohol. While the previously prepared alcoholates can generally 
only abstract oxygen, the mixture just referred to belongs to the class 
of very strong reducing agents. With the aid of this, it is possible to 
break up the double or centric union of the benzene ring, and thus 
prepare hydrogen derivatives of benzene. In this case the alcoholate 
does not act as a reducing agent as above, but the hydrogen effects the 
reduction : 

CH3.OH + Na = CH 3 .ONa + H 

The azoxy-compounds are yellow- to orange-red crystallisable sub- 
stances, which, like the nitro-compounds, are of an indifferent charac- 
ter ; but they are not volatile with steam, and cannot be distilled 
without undergoing decomposition. On reduction they yield first 
the azo-compounds, then the hydrazo-compounds, and finally two 
molecules of a primary amine. By heating with sulphuric acid, azoxy- 
benzene is converted into its isomer oxyazobenzene : 

C C H 5 . N— N . C 6 H 5 = C G H 5 . N=N . C 6 H 4 . OH 

O 



If an azoxy-compound is distilled carefully over iron filings, its oxygen 
atom is removed, and an azo-compound is formed : 

C 6 H 5 . N— N . C 6 H 5 + Fe = C 6 H 5 . N=N. C 6 H 5 + FeO 
O 

Azo-compounds may also be obtained directly from nitro-compounds, 
since they are reduced by sodium amalgam or an alkaline solution of 



AROMATIC SERIES 203 

stannous chloride (sodium stannous oxide). The latter reducing agent 
acts in accordance with this equation : 

ONa X3Na 

/ C 6 H 5 .N / 

2C 6 H 5 .N0 2 + 4Sn = || + 4SnO 

\ QH 5 .N \ 

Sodium stannate 

Azo-compounds may also be obtained by the oxidation of hydrazo- 
compounds : 

C 6 H 5 . NH . NH . C H, + O = C G H 5 . NzzN . C 6 H- + H 2 

The azo-hydrocarbons are orange-red to red crystalline substances 
which can be distilled without decomposition, differing in this respect 
from the azoxy-compounds. 

Experiment : A few crystals of azobenzene are heated in a 
test-tube to boiling, over a free flame. A red vapour is evolved, 
which again condenses to crystals on cooling. 

The azo-compounds thus differ in their stability from the very easily 
decomposable diazo-compounds, which also contain the group N = N, 
but it is in combination with only one hydrocarbon residue and an acid 
residue ; e.g. C (! H 5 .N = N . CI. 

By the reduction of an azo-compound, a hydrazo-compound is first 
formed and finally an amine. 



The hydrazo-compounds are formed by the reduction of azo-com- 
pounds with ammonium sulphide or zinc dust and an alkali. Zinc dust 
with caustic soda acts as follows : 

/ONa 
Zn + 2 NaOH = Zn< + H 2 
\ONa 

They may also be formed on the direct reduction of nitro-compounds 
in alcoholic solution by zinc dust and an alkali ; this method is used 
practically on the large scale. 

The hydrazo-compounds, in contrast with the azoxy-, and especially 
with the intensely coloured azo-compounds. are colourless. They are 
derived from hydrazine, NH 2 — NH 2 , in which one hydrogen atom of 
the two amido-groups has been replaced by a hydrocarbon radical. The 



204 SPECIAL PART 

basic character of hydrazine is so weakened by the presence of the 
negative hydrocarbon residues, that the hydrazo-compounds no longer 
possess a basic character. On oxidation hydrazo-compounds pass over 
to azo-compounds, a reaction which takes place slowly but completely, 
under the influence of the oxygen of the air. The hydrazo-compounds 
decompose, on heating, into azo-compounds and primary amines. 

2C C H 5 .NH.NH.C 6 H 5 =C 6 H 5 .N=N.C 6 H 5 + 2C (J H 5 .NH 2 . 

Experiment : A few crystals of hydrazobenzene are heated in 
a small test-tube to boiling; the colourless compound becomes 
red, azobenzene being formed. In order to show the presence 
of aniline, after cooling, the substance is shaken with water and 
the bleaching-powder test applied. 

If the hydrazo-compounds are treated with concentrated acids like 
hydrochloric or sulphuric acids, they are converted into derivatives 
of diphenyl : l 

C 6 H S .NH.NH.C 6 H S = NH 2 .C 6 H 4 .C 6 H 4 .NH 2 

p-Diamidodiphenyl = Benzidine 

The molecular transformation takes place essentially in para position 
to the imide (NH) groups. 

Experiment : Hydrazobenzene is covered with concentrated 
hydrochloric acid, and allowed to stand for about 5 minutes. 
It is then treated with water, and half the solution is made alkaline 
with caustic soda : the free benzidine is extracted several times 
with ether, the ether evaporated, and the substance crystallised 
from hot water. Leaflets of a silvery lustre are obtained. Melt- 
ing-point, 122 . The other half of the solution is treated with 
dilute sulphuric acid, upon which the difficultly soluble benzidine 
sulphate separates out. 

Benzidine differs from hydrazobenzene, in that it is a strong, di-acid 
primary base. It is prepared technically, since the azo dyes derived 
from it possess the important property of colouring unmordanted cotton 
fibre directly ; for most azo dyes the cotton must first be mordanted. 
The first representative of these dyes made was Congo Red, prepared 
from the bisdiazo-compound of benzidine and naphthionic acid. In con- 
sequence, the entire class of these dyes is called the " Congo Dyes." 

1 J- P*.36,93; J- 1863,424. 



AROMATIC SERIES 205 



/ 



NH 



C 6 H 4 .N=N.C 10 H 5 v 

\S0 3 H 

/NH 2 

\S0 3 H 

In a wholly analogous manner, from o-nitrotoluene and o-nitroanisol 
are prepared o-tolidine and dianisidine, respectively. 



/CH 3 /OCH 3 

| 6H3 \NH 2 ^Nnh, 

1 H / NH * c H / NH * 
\CH 3 \OCH 3 

Tolidine Dianisidine 

If, in hydrazo-compounds, the para position to the imido (NH) 
group is occupied as, e.g., in p-hydrazotoluene, then the benzidine 
transformation cannot occur. 

In such cases, derivatives of o- and p-amidodiphenyl amine are 
formed through the so-called " Semidine transformation." x 



CH 3 <^ _ \— NH— NH-/~" NcH 3 >- 




CH 8 -/~\-NH 2 




o-Semidine NH \ 


^)>-CH 3 


CH 3 . CO . NH— / \_NH— NH— / \ > 




CH 3 . CO . NH-/" ~\— NH— S~ 

N / \ 


\-NH 2 . 


p-Semidine 


s 



5. REACTION : PREPARATION OF A THIOUREA AND A MUSTARD OIL 
FROM CARBON DISULPHIDE AND A PRIMARY AMINE 

Example : Thiocarbanilide and Phenyl Mustard Oil from Carbon 
Disulphide and Aniline 

Thiocarbanilide : A mixture of 40 grammes of aniline, 50 
grammes of carbon disulphide, 50 grammes of alcohol, and 

1 B. 26, 681, 688, 699 ; A. 287, 97. 



206 SPECIAL PART 

10 grammes of finely pulverised potassium hydroxide is gently 
boiled for 3 hours on a water-bath in a flask provided with a 
long reflux condenser. The excess of carbon disulphide and 
alcohol is then distilled off, the residue treated with water, the 
crystals separating out are filtered off, and washed first with water, 
then with dilute hydrochloric acid, and finally with water. For 
the preparation of phenyl mustard oil, the crude product is used 
directly, after it has been dried on the water-bath. In order to 
obtain pure thiocarbanilide, 2 grammes of the dried crude product 
are recrystallised from alcohol. Large, colourless tablets are thus 
obtained, which melt at 154 . Yield, 30-35 grammes. If a 
mixture of equal parts, by weight, of aniline, carbon disulphide, 
and alcohol (40 grammes of each) placed in a flask provided 
with a reflux condenser is heated, with the addition of caustic 
potash, to gentle boiling on the water-bath for 10-12 hours, a 
better, almost quantitative yield of thiocarbanilide is obtained, 
although a longer time is required. After the heating, proceed 
as above. 

Phenyl Mustard Oil: 1 In a flask of about 400 c.c. capacity 
place 30 grammes of the crude thiocarbanilide, and treat with 
120 grammes of concentrated hydrochloric acid; the mixture is 
distilled by heating to the boiling-point of the acid, on a sand- 
bath, with a large flame under a hood. When only about 20 c.c. 
of the liquid remain in the flask, the distillation is discontinued. 
The distillate is treated with an equal volume of water, the mustard 
oil separated in a dropping funnel, dried with a little calcium 
chloride, and distilled. Boiling-point, 222 . Yield, almost quan- 
titative. 

Triphenyl Guanidine : The residue remaining in the flask after 
the distillation with hydrochloric acid is treated with 100 c.c. of 
water, and then allowed to stand for several hours, when colourless 
crystals of triphenylguanidine hydrochloride separate out. These 
are filtered off, and warmed with some dilute caustic soda solution. 
The salt is decomposed, and the free base obtained, which on 
recrystallising from alcohol forms colourless crystals. Melting- 
point, 143 . 

1 B. 15, 986; Z. 1869, 589. 



AROMATIC SERIES 20y 

Carbon disulphide acts upon primary amines to form symmetrical 
disubstituted thioureas, e.g. : 

/NHX 6 H 5 
CSS + 2 C 6 H 5 . NH 2 = C=S + H 2 S. 

\NH . C 6 H 5 

Diphenyl thiourea = Thiocarbanilide 

By the addition of caustic potash the elimination of hydrogen sul- 
phide is facilitated, so that the reaction takes place in a shorter time 
than without the use of the alkali. 

From the thioureas thus obtained the mustard oils may be prepared 
by heating with acids, as hydrochloric acid, sulphuric acid, phosphoric 
acid. The reaction takes place in accordance with the following 
equation : 



/^H.C 6 H 

csn 
\n 



5 

H 



- C 6 H 5 .N=C=S + C 6 H 5 .NH 2 . 

C 6 H 5 Phenyl mustard oil 



The primary amine formed in addition to the mustard oil combines 
with the acid. Besides this reaction a second one takes place, viz. : 
the amine formed acts upon some still undecomposed thiourea, result- 
ing in the formation of a guanidine derivative : 

/NH.C 6 H 5 /NH.C 6 H S 

CS + C 6 H 5 . NH 2 = C=N . C 6 H 5 + H 2 S. 

\NH.C 6 H 5 \NH.C 6 H 5 

Triphenyl guanidine 

/NH 2 
Since guanidine C~ NH is an extremely strong base, which, like 

\nh 2 

caustic potash and caustic soda, absorbs carbon dioxide from the air, 
the introduction of the three negative phenyl groups in the above com- 
pound has not neutralised the basic properties entirely, and it still has 
the power to form salts. 

The aromatic mustard oils are in part colourless liquids, in part crys- 
tallisable solids, the lower members are easily volatile with steam, and 
possess a characteristic odour. In chemical behaviour they are very 
active. If they are warmed for a long time with an alcohol, they com- 
bine with the alcohol, addition taking place, and a thiourethane is 
formed : 

C 6 H 5 . NCS + C 2 H 5 . OH = C 6 H 5 . NH . CS . OC 2 H 5 . 

Phenylthiourethane 



208 SPECIAL PART 

In the same way, ammonia and primary bases are added with the 
formation of a thiourea : 

/NH 2 



C 6 H 5 .NCS + NH 3 = CS 

Phenylthiourea 



NH.C 6 H 5 



/H.C 6 H 5 
C 6 H 5 . NCS + C 6 H 5 . NH 2 = CS 

\nh.c 6 h 5 

s-Diphenylthiourea 

Experiment : Treat 2 drops of phenyl mustard oil on a watch- 
glass with 2 drops of aniline, and warm gently over a small flame. 
On stirring the reaction-product after cooling, with a glass rod, 
the thiocarbanilide will solidify in crystals, from which in the 
above reverse reaction the mustard oil itself was prepared. 

By heating with yellow mercuric oxide, the sulphur is replaced by 
oxygen, and an isocyanate is formed, which may be easily recognised 
by its extremely disagreeable odour : 

C 6 H 5 . NCS + HgO = C 6 H 5 . NCO + HgS. 

Phenyl isocyanate 

Experiment : Heat \ c.c. of phenyl mustard oil in a test-tube 
with the same volume of yellow mercuric oxide for some time, 
until the oil boils. The yellow oxide is changed to the black 
sulphide, at the same time the extremely disagreeable odour of 
the phenyl isocyanate arises ; the vapour of the compound attacks 
the eyes, causing tears. 



6. REACTION; THE SULPHONATION OF AN AMINE 
Example : Sulphanilic Acid from Aniline and Sulphuric Acid 1 

To 100 grammes of pure concentrated sulphuric acid in a dry 
flask, 30 grammes of freshly distilled aniline are added gradually, 
with shaking; the mixture is heated in an oil-bath up to 180- 
190 , until, from a test-portion diluted with water and treated 

1 A. 60, 312 ; ioo, 163 ; 120, 132. 



AROMATIC SERIES 209 

with caustic soda, no aniline separates out : about 4-5 hours' 
heating will be necessary. The cooled reaction-mixture is poured, 
with stirring, into cold water, upon which the sulphanilic acid 
separates out in crystals. It is filtered off, washed with water, and 
recrystallised from water, with the addition of animal charcoal, if 
necessary. Yield, 30-35 grammes. 

When an aromatic compound is treated with sulphuric acid, a por- 
tion of the benzene-hydrogen is replaced by a sulphonic acid group, 
the reaction taking place in accordance with the equation below. The 
aliphatic compounds do not react in a similar manner. Under the 
preparation of benzene sulphonic acid, the details of the reaction will 
be discussed. 







/OH 

+ S0 2 : 

X)H 


/NH 2 

\s0 3 H 






C 6 H 5 


.NH 2 


+ H 2 0. 








p 


-Amidobenzenesulphonic 
sulphanilic acid 


acid 



In the above example, it happens, as in many cases, that the sulphonic 
acid group enters in the para-position to the amido-(NH 2 ) group. 
The amido sulphonic acids are colourless crystallisable compounds 
melting with decomposition ; they possess acid properties, i.e. in dis- 
solving in alkalies. The basic character of the amine is so greatly 
weakened by the introduction of the negative sulphonic acid group that 
the amido sulphonic acids cannot form salts with acids. They differ 

/ /NH 2 v 

in this from the analogous carbonic acids e.g., C 6 H/ , which 

\ \co.oh; 

Amidobenzoic acid 

dissolve in both acids and alkalies. 

The amido-sulphonic acids, since they are derivatives of a primary 
amine, may like them be diazotised by the action of nitrous acid ; upon 
this fact depends their great technical importance. If the diazo-com- 
pounds thus obtained are combined with amines or phenols, azo dyes 
are formed which contain the sulphonic acid group, and in the form of 
their alkali salts are soluble in water. Sulphanilic acid particularly, 
and its isomer, metanilic acid, obtained by the reduction of m-nitro- 
benzenesulphonic acid, as well as the numerous mono- and poly-sul- 
phonic acids derived from a and f3 naphthyl amines, find extensive 
technical application in the manufacture of azo dyes, 
p 



210 SPECIAL PART 



7. REACTION: REPLACEMENT OF THE AMIDO- AND DIAZO-GROUPS 
BY HYDROGEN 

Example : Benzene from Aniline 

Dissolve 5 grammes of aniline in a mixture of 15 grammes of 
concentrated hydrochloric acid and 30 c.c. of water ; cool with 
ice, and treat with a solution of 5 grammes of sodium nitrite in 
15 c.c. of water, until free nitrous acid may be recognised with 
starch-potassium-iodide paper. The diazobenzenechloride solu- 
tion thus obtained is allowed to flow carefully into a solution of 
10 grammes caustic soda in 30 c.c. of water contained in a 400 c.c. 
flask which is well cooled with ice. Further, dissolve 20 grammes 
of stannous chloride in 50 c.c. of water, and treat this solution 
with a concentrated solution of sodium hydroxide (2 parts to 3 of 
water), until the precipitate at first formed (stannous oxide) is 
redissolved in the excess of the alkali. Treat the alkaline diazo- 
benzene solution, well cooled with ice-water, gradually with small 
portions of the sodium-stannous oxide solution, previously well 
cooled, waiting after each addition until the lively evolution of 
nitrogen has ceased before adding more. When all the reducing 
liquid has been added, the flask is connected with a condenser, 
and the liquid heated to boiling. The benzene formed passes over 
first, and is collected in a test-tube. By a careful distillation from 
a small fractionating flask (without condenser), it is obtained per- 
fectly pure. Boiling-point, 8i°. Yield, 3-4 grammes. 

As already mentioned, under the preparation of methyl amine, the 
behaviour of the aliphatic primary amines toward nitrous acid is very 
different from that of the aromatic compounds. While the former yield 
alcohols with the elimination of nitrogen, the latter, in a mineral acid 
solution, under the influence of nitrous acid, yield diazo-compounds, 
discovered by Peter Griess, in the form of their mineral acid salts. 

CH 3 . NH 2 + NOOH = CH 3 . OH + N 2 + H 2 

C C H 5 ,NH 2 + NOOH + HC1 = C H 5 . N=N . CI + 2 H 2 

Diazobenzene chloride 

It has been held that the mother substance of the diazo-compounds, 
— free diazobenzene — possessed the constitution: 



AROMATIC SERIES 211 



in in 
C 6 H 5 . N=N - OH 

In accordance with which the diazo salts were expressed by : 

C 6 H 5 . NzzN . CI = Diazobenzene chloride, 

C 6 H 5 . NzzN . N0 3 = Diazobenzene nitrate, 

C 6 H 5 . N=N . O . S0 2 . OH = Diazobenzene sulphate. 

More recently this view has been abandoned, and the one proposed 
earlier by Blomstrand taken up. It is, however, not accepted generally. 
According to this conception the above salts are represented thus : 

in in in 

V /N V ^N V /N 

C 6 U 5 .N( ;C 6 H 3 .Nf ;C 6 H 5 .Nf 

\C1 \NO.3 \O.S0 2 .OH 

In accordance with this view the diazotising process consists in re- 
placing the three hydrogen atoms combined with a nitrogen atom 
having a valence of 5, by a trivalent nitrogen atom : 



C 6 H,.N 



\ 



+ N 



OOH 



CI 

Aniline hydrochloride 



2H 2 o + c 6 h,n/ 



To emphasise the similarity to ammonium compounds, in which the 
valence of the nitrogen atom is probably 5, the diazo salts are called 
diazonium salts. The diazo-compounds can also form double salts, e.g. : 

C 6 H 5 .N=N.Cl.AuCl 3 and (C G H 5 . NzzN . Cl) 2 . PtCl 4 

Diazobromides have the power of taking up two atoms of bromine to 
form perbromides : 



C 6 H 5 . N=N . Br + Br 2 



N 

Diazobenzene perbromide 



Experiment : Dissolve 1 c.c. of aniline in an excess of hydro- 
chloric acid, diazotise as above, and add 1 c.c. of bromine dissolved 
in a water solution of hydrobromic acid, or in a concentrated 
solution of potassium bromide. A dark oil separates out, from 
which the solution is decanted. It is washed several times with 
water ; on cooling, it solidifies to crystals. 



212 SPECIAL PART 

If ammonia is allowed to act on the perbromide, diazobenzeneimide 
is obtained : 

C 6 H 5 .NBr.NBr 2 + NH 3 = C 6 H 5 .N + 3 HBr 

\n 

Diazobenzeneimide 

Experiment : The perbromide just obtained is covered with 
water, and concentrated ammonium hydroxide added to it. A 
vigorous reaction takes place with the formation of an oil possess- 
ing a strong odour (diazobenzeneimide). 

Under the influence of alkalies the diazonium compounds yield salts, 
thus acting like acids. 

C 6 H 5 . N 2 . CI + 2 NaOH = C 6 H 5 . N 2 . ONa + NaCl + H 2 

These can exist in two isomeric modifications. The one primarily 
obtained is characterised by the fact that in alkaline solution it unites 
with phenols to form azo dyes ; while the second modification obtained 
by a longer action of the alkali, at higher temperature if necessary, does 
not possess this property at all, or only in a slight degree. If they 
(the latter) be treated with acids, they are converted back into the 
diazonium salts, and now have the property of combining with phenols 
to form azo dyes. In spite of numerous experiments the constitution of 
these substances is not wholly clear. 

Bamberger's view is that the diazonium salt first obtained should be 
represented by 

V III 

C 6 H 5 . N = N 
ONa 

and that this, through the further action of the alkali, undergoes a 
molecular transformation into C 6 H 5 .N = N . ONa. 

Hantzsch, on the other hand, ascribes to both salts the constitution 
C 6 H 5 . NzzN . ONa, and explains their differences by stereo-chemical 

formulae : 

C 6 H 5 .N C 6 H 5 .N 

II II 

N - ONa NaO . N 

Antidiazo compound Syndiazo compound 

Does not unite with phenols Unites with phenols 

The salts of the diazo-com pounds formed with acids are, in most cases, 
colourless, crystallisable substances, easily soluble in water, insoluble 



AROMATIC SERIES 213 

in ether. In order to prepare them in the solid condition, various 
methods may be used. Thus, e.g., the very explosive diazobenzene- 
nitrate may be obtained in colourless needles by conducting gaseous 
nitrous acid into a well-cooled pasty mass of aniline nitrate and water, 
and treating the diazo-solution with alcohol and ether. In general, the 
solid diazo-salts may be prepared by adding to an alcoholic solution of 
the amine that acid the salt of which is desired, and then treating the 
well-cooled mixture with amyl nitrite : x 

C G H 5 . NH 2 + N0 2 . C, 5 H n + HC1 = C 6 H S . N=N . CI + C 5 H n . OH + H 2 

Amyl nitrite Amyl alcohol 

If the solid diazo-compound does not separate out at once, ether is 
added. On heating, the dry diazo-salts decompose either, as in the 
case of diazobenzene nitrate, with explosion, or a sudden evolution of 
gas takes place without detonation. A few diazo-compounds are so 
stable that they may be recrystallised from water. 

In rare cases only, in working with diazo-compounds, is it necessary 
to isolate them in a pure condition ; generally, the very easily prepared 
water solutions are used. These compounds were formerly obtained 
by passing gaseous nitrous acid into a salt of the amine until it was 
diazotised. But at present this method is employed only in rare cases ; 
the free nitrous acid obtained from sodium nitrite is used. In order to 
diazotise an amine, a solution of it in a dilute acid — most frequently 
hydrochloric acid or sulphuric acid — is first prepared. Theoretically, 
two molecules of a monobasic acid are required to diazotise one mole- 
cule of a monamine : 

C G H 5 . NH 2 -f- NaN0 2 + 2 HC1 = C G H, . N 2 . CI + NaCl + 2 H 2 

but an excess is always taken, — not less than three molecules of hydro- 
chloric acid or two of sulphuric acid to one molecule of a monamine. 
In many cases, the hydrochloride or sulphate of the amine is difficultly 
soluble in water. Under these conditions, it is not necessary to add 
water until the salt is entirely dissolved, but the solution of the nitrite 
may be poured into the pasty mass of crystals ; when the undissolved 
salt is diazotised, it passes into solution. For the diazotisation of one 
molecule of a monamine, one molecule of sodium nitrite is necessary, 
theoretically ; but since the commercial salt is never perfectly pure, it 
is advisable to weigh off from 5-10 % more than the calculated amount, 
and to determine by the method given below when a sufficient quantity 



1 B. 23, 2994. 



214 SPECIAL PART 

of this has been added. The nitrite is dissolved in water, generally 
5-10 parts of water to 1 part of salt. The nitrite solution must be 
added gradually to the amine solution, and the liquid must not be 
allowed to become warm. In many cases, the experimenter is often 
too careful, in that he cools the amine solution with a freezing mixture, 
and adds the nitrite solution drop by drop from a separating funnel. 
Frequently it is sufficient to place the solution in a water-bath filled 
with cold water, or ice is thrown into the water, or the amine solution 
is cooled by ice. It is very convenient to cool the solution, not from 
without, but by throwing into it from time to time small pieces of ice. 
The nitrite solution may be poured directly from a flask. If the addi- 
tion causes evolution of gas bubbles or vapours of nitrous acid, the 
temperature of the solution must be lowered and the nitrite added more 
slowly. In order to be cognisant of the course of the reaction, as well 
as to be able to determine when it is completed, starch-potassium-iodide 
paper, prepared as follows, is used : 

A piece of starch the size of a pea is finely pulverised, and added to 
200 c.c. of boiling water ; it is boiled a short time, with stirring. After 
cooling, a solution of a crystal of potassium iodide the size of a lentil, 
in a little water, is added to it. With this mixture, saturate long strips 
of filter-paper 3 cm. wide ; the strips are dried by suspending them 
from a string in a place free from acids. After drying, the strips are 
cut up and preserved in a closed vessel. 

In order now to diazotise an amine, the cooled solution is first 
treated with a small portion of the nitrite solution ; it is well stirred, 
and a drop of it transferred with a clean glass rod to the starch- 
potassium-iodide paper. If the nitrous acid is already used up in the 
diazotisation, no dark spots appear, and further portions of the sodium 
nitrite may be added, the test is again repeated, and so on. But if a 
dark spot is formed at once, the nitrous acid is still present ; and in 
this case, before more of the nitrite is added, one waits until the reaction 
has been completed, and so on. After the addition of three-fourths 
of the nitrite solution, larger quantities may be added at one time, but 
toward the end of the reaction small quantities must again be employed. 
The diazotisation is ended when, after standing some time, the mixture 
shows the presence of nitrous acid. Since the diazotisation of the last 
portions of the amine often requires some time, the addition of the 
nitrite is not discontinued at once, even if after one minute the test 
for nitrous acid is obtained, but the solution is allowed to stand 
5-10 minutes, and is then tested again. At times, it happens that the 



AROMATIC SERIES 215 

weighed-off quantity of sodium nitrite is apparently not sufficient to 
complete the diazotisation, and that even after the addition of a fresh 
quantity, the test will not show the presence of nitrous acid. This 
phenomenon has its cause generally in the fact that the acid (hydro- 
chloric or sulphuric) has been used up, and consequently the nitrite 
cannot enter into the reaction. Thus, in case the weighed-off amount 
of sodium nitrite is not sufficient, some acid is first added to a small 
portion of the liquid, and this is then tested to determine whether the 
desired reaction has taken place. Further, often the diazo-solution 
becomes cloudy toward the end of the reaction, or a precipitate sepa- 
rates out. This is the diazoamido-compound ; its formation is also 
caused by the lack of free acid. On the addition of acid and solution 
of the nitrite, the precipitate disappears. The replacement of the 
diazo-group by hydrogen in the above reaction takes place in accord- 
ance with the following equation : 

C G H 5 .N 2 .OH + H 2 = C 6 H 6 + N 2 + H 2 1 

In this way it is possible in many cases to replace a primary amido- 
group by hydrogen. Obviously, such a reaction is superfluous, if, as 
in the above case, the amine is obtained by the nitration of the hydro- 
carbon and the reduction of the nitro-compound. But there are cases 
in which an amine is not obtained in this way, and where it is of 
importance to prepare the amido-free compound (see below). 

The replacement of a diazo-group by hydrogen may be effected by 
other reducing agents. If, e.g., a diazo-compound is boiled with 
alcohol, the latter is converted into aldehyde, thus liberating two 
hydrogen atoms, by which the diazo-compound is reduced : 

C G H 5 . N 2 . OH + CH 3 . CH 2 . OH = C 6 H 6 + N 2 + CH 3 . CHO + H 2 

Aldehyde 

The reaction is effected either by conducting gaseous nitrous acid into 
the boiling alcohol solution of the amine, or by heating the amine with 
alcohol saturated with ethyl nitrite ; or the boiling alcohol solution of the 
amine, acidified with sulphuric acid, may be treated with sodium nitrite. 

At this place, two examples may be mentioned which illustrate the 
theoretical as well as the practical value of the reaction : by the oxida- 
tion of a mixture of aniline and p-toluidine, there is formed a complex 
dye, para-fuchsine, the constitution of which was unknown for a long 
time. This was first explained by E. and O. Fischer. They heated 
the diazo-compound of the leuco-base of the dye, paraleucaniline with 



1 B. 22, 587. 



2l6 SPECIAL PART 

alcohol, which gave the mother substance — the hydrocarbon triphenyl 
methane (A. 194, 270). 

As an example of the preparation value of the reaction, the following 
case is cited : 

No method is known by which m-nitrotoluene can be prepared by 
the nitration of toluene ; this results in the formation of the o- and 
p-compounds only. In order to obtain the m-nitrotoluene, the start- 
ing-point is p-toluidine. This is nitrated, upon which a nitrotoluidine 
of the following constitution is obtained : 

CH, 




NH 2 

If the amido-group is replaced by hydrogen, using the method last 
described, the desired m-nitrotoluene is obtained. 

By boiling a diazo-compound with alcohol the reaction may take place 
in a different way ; at times the diazo-group is not replaced by hydrogen, 
but by the ethoxy (-OC 2 H 5 ) group, thus giving rise to a phenol ether. 

X . NzzN . S0 4 H + C 2 H 5 . OH = X . OC 2 H 5 + N 2 + H 2 S0 4 

In conclusion, special attention is called to the fact that not only 
aniline and its homologues can be diazotised, but all the derivatives of 
these, as the nitro-amines, halogen-substituted amines, amido-alde- 
hydes, amido-carbonic acids, etc. 

8. REACTION: REPLACEMENT OP THE DIAZO-GROUP BY 
HYDROXYL 

Example : Phenol from Aniline 

Pour 20 grammes of concentrated sulphuric acid as rapidly as 
possible, with stirring, into 50 grammes of water ; to the hot 
solution add 10 grammes of freshly distilled aniline, with stirring, 
by allowing it to flow down the side of the beaker, then add 
100 c.c. of water. After the hot liquid has been cooled by im- 
mersion in cold water, it is treated with a solution of 8.5 grammes 
of sodium nitrite in 40 c.c. of water, until it shows a blue spot on 
starch-potassium-iodide paper. The diazobenzene sulphate solu- 



AROMATIC SERIES 21? 

tion thus obtained is gently heated (40-5 o°) for half an hour on 
the water-bath, the phenol is then distilled over with steam, and 
the distillate, after being saturated with salt, is extracted several 
times with ether. The ethereal solution is allowed to stand for 
some time over fused sodium sulphate. The ether is then evapo- 
rated, and the residue of phenol is subjected to distillation in a 
small flask. Boiling-point, 183 . Yield, 7-8 grammes. 

The liquid remaining back in the flask after the steam distilla- 
tion is filtered hot. On cooling, a small quantity of oxydiphenyl 
crystallises out. 

If a diazo-compound is heated with water, it will pass over to a 
phenol with the evolution of nitrogen, e.g. : 

C 6 H 5 . N=N . O . S0 2 . OH + HOH = C 6 H 5 . OH + N 2 + H 2 S0 4 

For this reaction the diazosulphate is most advantageously used. Under 
certain circumstances, the diazochloride may also be employed. But 
the use of the diazonitrate is avoided, since, in this case, the nitric acid 
liberated, acting upon the phenol, readily forms nitro-compounds. In 
many cases, it is more convenient not to isolate the diazo-compound, 
but to add a water solution of the calculated amount of sodium nitrite 
to a boiling solution of the amine in dilute sulphuric acid. The diazo- 
tisation of the substance and the immediate decomposition of the diazo- 
compound take place in one operation. 

The same reactions are also applicable to substituted amines, like 
amido- carbonic acids, amido-sulphonic acids, halogen substituted 
amines, etc. 

The oxydiphenyl obtained as a by-product is formed in consequence 
of the action of some of the undecomposed diazo-compound on phenol : 

C 6 H 5 . N 2 . S0 4 H + H . QH 4 . OH = C 6 H 5 . C C H 4 . OH + H 2 S0 4 + N 2 
(Compare B. 23, 3705.) 

9. REACTION: REPLACEMENT OF A DIAZO-GROUP BY IODINE 

Example : Phenyl Iodide from Aniline 

{Phenyliodidechloride ; Iodoso-benze?ie, Phenyl iodite, and 
Diphenyliodonium iodide?} 

A solution of 10 grammes of aniline in a mixture of 50 grammes 
of concentrated hydrochloric acid and 150 grammes of water 



218 SPECIAL PART 

cooled with ice-water is gradually treated with a solution of 8.5 
grammes of sodium nitrite in 40 c.c. of water, until a test will give 
a blue colour to the starch-potassium-iodide paper. The diazo- 
solution is then treated in a flask, not too small, with a solution of 
25 grammes of potassium iodide in 50 c.c. of water, the mixture is 
allowed to stand several hours, being cooled by water, finally it is 
gently heated on the water-bath until the evolution of nitrogen 
ceases. The liquid is made strongly alkaline with caustic soda or 
caustic potash, and the iodobenzene distilled over with steam ; 
the steam delivery tube should reach almost to the bottom of the 
flask. The iodobenzene is separated from the water in a dropping 
funnel, dried with calcium chloride and redistilled. Boiling- 
point, 189-190 . Yield, about 20 grammes. 

If a diazoiodide is heated, the diazo-group is replaced by iodine, the 
reaction taking place smoothly in most cases. 

C 6 H 5 .N 2 .i = C 6 H 5 .I + N 2 

The reaction is effected by diazotising the amine in a hydrochloric acid 
or sulphuric acid solution, and then treating it with potassium iodide. 
From the diazochloride or diazosulphate there is formed a diazoiodide, 
the reaction, in many cases, taking place at the ordinary temperature ; 
in others, on heating, as above. Since the reaction occurs without 
difficulty, it is used as the method of preparation of many iodides. 

The aromatic iodides possess the noteworthy property of combining 
with two atoms of chlorine, the iodine previously univalent becoming 
trivalent : 

C 6 H 5 .i + Cl 2 = C 6 H 5 . n iCl 2 i 

Phenyliodidechloride 

Experiment : The phenyl iodide obtained is dissolved in five 
times its volume of chloroform, the solution is cooled by ice-water, 
and a current of dry chlorine is passed into it from a very wide 
delivery tube, until no more is absorbed. The crystals separating 
out are filtered off, washed with a fresh quantity of chloroform, 
spread out in a thin layer on a pad of filter-paper, and allowed to 
dry in the air. 



J. pr. 33, 154. B. 25, 3494 ; 26, 357 ; 25, 2632. 



AROMATIC SERIES 219 

If caustic soda is allowed to act on an iodochloride, the two chlorine 
atoms are replaced by one oxygen atom, and an iodoso-compound is 
obtained : 

C 6 H S . IC1, + H 2 = C 6 H S . 1=0 + 2 HC1 

Iodosobenzene 

Besides this reaction another takes place, resulting in the formation of 
an iodonium base. This formation is probably due to the fact that a 
small part of the iodosobenzene is oxidised to phenyl iodite, and this 
condenses with iodosobenzene, iodic acid being eliminated : 

/OH 
C G H 5 .I< + I0 2 .C G H, =C,.H 5 - I - C G H, + HIO3. 
\OH I 

Hypoth. Iodoso- OH 

benzene hydrate Diphenyliodonium hydroxide 

This base is present in the alkaline solution filtered off from the iodoso- 
benzene. If the filtrate, be treated with sulphur dioxide, this reduces 
the iodic acid to hydriodic acid, which, combining with the iodonium 
base, forms an iodide insoluble in cold water : 

HIOo + 3 SO, = HI + 3 S0 3 

C 6 H S - I - C G H 5 m 

|_ = C 6 H 5 - I - C 6 H S + H 2 

[oh+hJi I 



I 

Experiment : The iodochloride is carefully triturated with dilute 
caustic soda in a mortar (for 1 gramme of the iodochloride, use a 
solution of 0.5 gramme sodium hydroxide in 4 grammes of water), 
and allowed to stand over night. The iodosobenzene is then 
filtered off, washed with water, and pressed out on a porous plate. 

The alkaline filtrate is treated with a solution of sulphur dioxide 
until it smells strongly of it. The precipitate formed is filtered 
off and dissolved in hot water. On cooling, colourless needles of 
diphenyliodonium iodide are obtained. 

The iodoso-compounds have the power of uniting with acids to form 

/OH 
salts, in which they act like a di-acid base, e.g., C H-.I<^ 

\OH 

Experiment : Several grammes of iodosobenzene are dissolved 
with heat in as small a quantity of glacial acetic acid as possible ; 



220 SPECIAL PART 

the solution is evaporated on the water-bath to dryness, in a watch- 
glass, or shallow dish. The solid residue is pulverised and re- 
crystallised from a little benzene. Iodosobenzene acetate is thus 

obtained, 

/OOC.CH3 
C 6 H 5 .I<: 

\OOC.CH3 

in the form of colourless prisms, melting at 15 7 . 

The iodoso-compounds, on treatment with hydriotlic acid, are reduced 
to iodides, with a separation of iodine. 

C G H 5 . 10 + 2 HI = C 6 H 5 . 1 + I 2 + H 2 

This reaction is used for the quantitative determination of iodoso- 
oxygen. 

Experiment : Some potassium iodide is dissolved in water, 
acidified with dilute sulphuric acid, or acetic acid, and a few 
grains of iodosobenzene are added. The iodine separates out as 
a brown precipitate. 

If an iodoso-compound is heated carefully to ioo°, it passes over to 
an iodite (Jodoverbindung) : 

2C G H 5 .IO = C (; H 5 .I0 2 + C 6 H 5 .I 

Phenyl iodite Phenyl iodide 

The same compound may also be obtained by treating an iodoso- 
compound with steam. 

Experiment : Iodosobenzene is treated in a flask with enough 
water to form a thin paste. Into this steam is conducted (appa- 
ratus for distillation with steam), until no more phenyl iodide 
passes over with the steam and all the iodosobenzene has been 
dissolved. If the phenyliodite formed does not dissolve com- 
pletely, water is added until solution takes place. The solution 
is then evaporated on the water-bath until a test-portion cooled 
off yields an abundant crystallisation of phenyl iodite. 

The iodites, like the iodoso-compounds, puff up and suddenly decom- 
pose on heating. (Try it.) They also abstract iodine from hydriodic 
acid, and in double the quantity as compared to the similar action of 
the iodoso-compounds. 






AROMATIC SERIES 221 

C 6 H 5 . I0 2 + 4 HI = C 6 H 5 I + 4 I + 2 H 2 

They do not form salts with acids. 

The iodonium bases are prepared most conveniently by the action 
of silver oxide on a mixture of equal molecules of iodoso and iodite 
compounds : 

C G H . . 10 + C 6 H 5 . I0 2 + AgOH = C 6 H 5 .?. C 6 H S + AgI0 3 

OH 

They are soluble in water, show a strong alkaline reaction like the 

sulphonium and ammonium compounds, and give with halogen hydracids 

precipitates of the corresponding salts. If the dried salts be heated, 

they decompose into two molecules of the hydrocarbon substitution 

product, e.g. : 

m 
C 6 H 5 .I.C G H 5 = 2C G H 5 I 

j 

I 

Experiment : The diphenyliodonium iodide obtained as a by- 
product in the preparation of iodosobenzene is heated carefully in 
a test-tube over a small flame. Suddenly the substance begins to 
melt in one place ; the fusion increases, without the need of 
further heating, and the whole mass boils up. Iodobenzene, easily 
recognised by its odour, is obtained. 



10. REACTION: REPLACEMENT OF A DIAZO-GROUP BY CHLORINE, 
BROMINE, OR CYANOGEN 

Example : p-Tolyl Nitrile from p-Toluidine 

Dissolve 50 grammes of copper sulphate in 200 grammes of 
water in a 2-litre flask by heating on the water-bath; then add 
gradually, with continuous heating, a solution of 55 grammes of 
potassium cyanide in 100 c.c. of water. Since cyanogen is 
evolved, the reaction must be conducted under a hood, with a 
good draught, and the greatest care taken not to breathe the 
vapours. 

While the cuprous cyanide solution is further gently heated up 
to about 60-70 on the water-bath, the diazotoluenechloride solu- 



222 SPECIAL PART 

tion is prepared in the following way : 20 grammes of p-toluidine 
are heated with a mixture of 50 grammes of concentrated hydro- 
chloric acid and 150 c.c. of water until solution takes place; the 
liquid is then quickly immersed in cold water and vigorously 
stirred with a glass rod, in order that the toluidine hydrochloride 
may separate out in as small crystals as possible. A solution of 
16 grammes of sodium nitrite in 80 c.c. of water is then added 
to the amine hydrochloride, cooled by ice-water, until a perma- 
nent reaction of nitrous acid upon the starch-potassium-iodide 
paper is obtained. The diazotoluene chloride thus formed is 
poured from a flask into the cuprous cyanide solution, with 
frequent shaking. After the addition of the diazo-solution, which 
should require about 10 minutes, the reaction mixture is heated 
on the water-bath for about a quarter-hour. The tolyl nitrile is 
then distilled over with the steam. This operation must also be 
done under a hood with a good draught, since hydrocyanic acid 
passes over. The nitrile distils as a yellow oil, which after some 
time solidifies in the receiver. It is separated by decanting the 
water, pressed upon a porous plate, and purified by distillation. 
If the oil will not solidify, the entire distillate may be taken up 
with ether, the ethereal solution shaken with caustic soda solution 
to remove the cresol, and then, after evaporating the ether, the 
residue remaining is distilled directly, or, in case it is solid, it is 
pressed out on a porous plate, as above, and then distilled. Boiling- 
point, 2 1 8°. Yield, about 15 grammes. 

The diazo-group cannot be replaced in the same way by iodine as 
by chlorine, bromine, or cyanogen. If a water solution of a diazo- 
chloride, -bromide, or -cyanide is heated, a phenol is formed, as is also 
the case on heating a diazo-sulphate : 

C 6 H 5 . N 2 . CI + H 2 = C 6 H 5 . OH + N 2 + HC1 

To Sandmeyer 1 we are indebted for the important discovery that, if 
the heating be done in the presence of cuprous chloride, bromide, or 
cyanide, the reaction taking place is analogous to the one by which 
phenyl iodide is formed : 



1 B. 17, 1633 and 2650 ; 18, 1492 and 1496. 



AROMATIC SERIES 223 

C 6 H,.N,.C1 =C e H 5 .Cl +N, 1 . .. ... 

C H . Nl. Br = C H .Br +N In the ?"*«"* of ** 

C*H, . N*. CN = C^.CN + n| j coms P° ndln g cu P rous salt - 

The manner in which the cuprous salts act is not known ; in any 
case they unite first with a diazo-compound to form a double salt, 
which plays a part in the reaction. 

The reaction in the above preparation of cuprous cyanide takes place 
in accordance with the following equation : 

CuS0 4 + 2 KCN = CuCN 2 + K 2 S0 4 
2 CuCN 2 = Cu 2 CN 2 + 2 CN 

In order to replace the diazo-group by chlorine or bromine, the 
above method is followed exactly. A diazo-solution is first prepared, 
and gradually added to a heated solution of cuprous chloride or bromide. 
With easily volatile chlorine or bromine compounds, it is desirable to 
use a reflux condenser, and to allow the diazo-solution to flow in from a 
dropping funnel. In some cases it is more advantageous not to use 
a previously prepared diazo-solution, but to proceed as follows : The 
amine is dissolved in an acid solution of a copper salt ; this is heated, 
and to the hot solution, the solution of nitrite is added from a dropping 
funnel. The diazotisation and replacement of the diazo-group then 
takes place in one reaction. If the reaction-product is not volatile with 
steam, it may be obtained from the reaction-mixture by filtering, or 
extracting with ether. 

The Sandmeyer reaction is capable of general application. Since 
the yield of the product is generally very good, for many substances it 
is used as a method of preparation. It should be finally pointed out 
that by the replacement of the diazo-group by cyanogen a new carbon 
union takes place. 



11. REACTION: (a) REDUCTION OF A DIAZO-COMPOUND TO A HY- 
DRAZINE. (3) REPLACEMENT OF THE HYDRAZINE-RADICAL BY 
HYDROGEN 

Examples : (a) Phenyl Hydrazine from Aniline 
{b) Benzene from Phenyl Hydrazine 

(a) Add io grammes of freshly distilled aniline to ioo c.c. of 
concentrated hydrochloric acid in a beaker, with stirring ; aniline 
hydrochloride partially separates out in crystals. To the mixture, 



224 SPECIAL PART 

cooled with ice, add slowly from a dropping funnel, a solution of 
10 grammes of sodium nitrite in 50 c.c. of water, until a test with 
starch-potassium-iodide paper shows free nitrous acid. In this 
case the strong acid solution must not be brought directly upon 
the test-paper, but a test-portion is diluted with water in a watch- 
glass and then the test applied. To the diazo-solution add, with 
stirring, a solution of 60 grammes of stannous chloride in 50 c.c. 
of concentrated hydrochloric acid cooled with ice ; a thick paste of 
crystals of phenyl hydrazine hydrochloride separates out. After 
standing several hours this is filtered off with suction (Biichner 
funnel and filter-cloth), the precipitate is pressed firmly together 
on the filter with a pestle ; it is then transferred to a small flask 
and treated with an excess of caustic soda solution. Free phenyl 
hydrazine separates out as an oil, it is taken up with ether, the 
ethereal solution dried with ignited potash, and the ether evap- 
orated. For the later experiments the phenyl hydrazine thus 
obtained can be used directly. If it is desired to purify the sub- 
stance, the best method is to distil it in a vacuum, or it can be 
cooled by a freezing- mixture, and the portions remaining liquid 
are poured off. Yield, about 10 grammes. 

Since the diazotisation in a strong hydrochloric acid solution 
as well as the filtration of strongly acid liquids is liable to mis- 
carry, it is better to perform the experiment as follows : Dissolve 
10 grammes of freshly distilled aniline in a mixture of 30 grammes 
of concentrated hydrochloric acid and 75 c.c. of water and diazo- 
tise it with a solution of 8 grammes of sodium nitrite in 30 c.c. 
of water, the beaker being cooled with ice-water. The diazo- 
solution is saturated with finely pulverised salt (about 30 grammes) 
with shaking ; the solution is poured off from any undissolved salt, 
and being cooled with ice is treated with a cold solution of 60 
grammes of stannous chloride in 25 grammes of concentrated 
hydrochloric acid. After several hours' standing, the phenyl- 
hydrazine hydrochloride separates out, this is filtered off with 
suction, washed with a little saturated salt solution, pressed out 
on a porous plate, and treated as above. 

{b) In a 1 -litre flask provided with a dropping funnel and con- 



AROMATIC SERIES 



225 



denser (Fig. 68) 150 grammes of water and 50 grammes of cop- 
per sulphate are heated to boiling, then from the funnel add 
gradually a solution of 10 grammes of free phenyl hydrazine in 
a mixture of 8 grammes of glacial acetic acid and 75 grammes of 
water. The oxidation of the phenyl hydrazine proceeds with an 
energetic evolution of nitrogen ; the benzene is immediately dis- 
tilled over with steam and collected in a test-tube. By another 
careful rectification from a small fractionating flask (without con- 




FlG. 68. 

denser), pure benzene, boiling at 8i°, is obtained. Yield, about 
5 grammes. 

Monosubstituted hydrazines of the type of phenyl hydrazine may 
be obtained according to the method of V. Meyer and Lecco, 1 by 
reducing the diazo-compounds with stannous chloride and hydrochloric 
acid: 



2 H. 



:C G H 5 .NH.NH 2 , HC1 

Phenyl hydrazine hydrochloride 



The reaction is always conducted as above : The amine is diazotised 
in a strong hydrochloric acid solution, and then a solution of stannous 
chloride in strong hydrochloric acid is added to it. Since the hydro- 
chlorides of the hydrazines are difficultly soluble in concentrated 
hydrochloric acid, these separate out directly on the addition of the 



1 B. 16, 2976. 
Q 



226 SPECIAL PART 

stannous chloride, and can easily be obtained pure by filtration, as 
above. 

The reduction of the diazo-compounds to hydrazines may be ac- 
complished by the method of Emil Fischer 1 which led to the dis- 
covery of this class of compounds, and also by another method. If 
neutral sodium sulphite is allowed to act on a diazo-salt, the acid 
radical of the diazo-compound is replaced by a residue of sulphurous 
acid, e.g. : 

C G H 5 . N 2 . CI + NaSOg . Na = C 6 H 5 . N 2 . S0 3 Na + NaCl 

Sodium diazobenzenesulphonate 

If this salt is now reduced with sulphurous acid, or with zinc dust 
and acetic acid, it takes up two atoms of hydrogen and is converted 
into a hydrazine sulphonate : 

C G H 5 . N 2 . S0 3 Na + H 2 = C G H 5 . NH . NH . S0 3 Na 

Sodium phenyl hydrazine sulphonate 

If this is heated with hydrochloric acid, the sulphonic acid group is 
split off, and phenyl hydrazine hydrochloride is formed, which, on 
evaporation, crystallises out : 

C G H 5 .NH.NH.S0 3 Na + HCl + HOH = C G H 5 .NH.NH 2 ,HCI+NaHS0 4 . 

According to this method, which is slower, but cheaper than the 
former, phenyl hydrazine is prepared on the large scale. 

The monosubstituted hydrazines possess a basic character ; in spite 
of the fact that they contain two ammonia residues, they combine with 
only one molecule of a monobasic acid, e.g. : 

C 6 H 5 .NH.NH 2 ,HC1. 

Phenyl hydrazine hydrochloride 

Phenyl hydrazine reacts with aldehydes and ketones, the two hydro- 
gen atoms of the amido-groups unite with the oxygen atom- of the 
CHO- or CO-groups, and are eliminated as water: 2 

C 6 H 5 . CHO + C G H 5 . NH . NH 2 = C G H 5 . CH=N . NH . C G H 5 + H 2 

Benzaldehyde Benzylidenephenyl hydrazone 

C e H 5 x 
C 6 H S . CO . C G H 5 + C G H 5 . NH . NH, = >C= N • NH ■ C 6 H s + H 2°- 

C fl H/ 

Benzophenone 



1 A. 190, 67. 2 B. 16, 2976. 



AROMATIC SERIES 



227 



This reaction can be used for the recognition and detection of 
aldehydes and ketones. In order to prepare a hydrazone, formerly a 
solution of 1 part of phenyl hydrazine hydrochloride and i| parts of 
crystallised sodium acetate in 10 parts of water was used as a reagent. 
If this is added to an aldehyde or ketone, there is formed, in many cases 
at the ordinary temperature, but in others only on heating, the hydra- 
zone. Since, at present, perfectly pure free phenyl hydrazine may be 
purchased in the market, a mixture of equal volumes of phenyl hydra- 
zine and 50 % acetic acid, diluted with three times its volume of water, 
is used as the reagent. 

Experiment : To a mixture of 4 drops of phenyl hydrazine and 
5 c.c. of water, add 3 drops of glacial acetic acid. To this is 
added 2 drops of benzaldehyde (from a glass rod), and the mix- 
ture shaken. At first there appears a milky turbidity, but very 
soon a flocculent precipitate of benzylidenephenyl hydrazone sepa- 
rates out. The smallest quantity of benzaldehyde may be recog- 
nised in this way. 

Phenyl hydrazine is of extreme importance in the chemistry of the 
sugars for the separation, recognition, and transformation of the dif- 
ferent varieties of the sugars. Without this reagent, the fundamental 
explanations of the last few years in this field could scarcely have been 
made. If one molecule of phenyl hydrazine is allowed to act on one 
molecule of a sugar, a normal hydrazone is formed, e.g. : 

CH 2 . OH (CH . OH) 4 . CHO + C C H 5 . NH . NH 2 

Grapesugar = CH 2 . OH (CH . OH) 4 . CH + H 2 

N-NH.C 6 H 5 . 

But if the phenyl hydrazine is used in excess, it acts as an oxidising 
agent toward the sugar, extracting water, e.g., in the above case, 
one of the secondary alcohol (CH.OH) groups adjoining the alde- 
hyde (CHO) group is oxidised to a ketone group, which again reacts 
with the hydrazine. The compound thus obtained is called an "Osa- 
zone." In the above example, there is obtained a compound of this 
composition : 

CH, . OH . (CH . OH) 3 . C — CH=N . NH . C 6 H- 

II 
N 

I 
• NH.CH, 



228 SPECIAL PART 

If this compound is heated with hydrochloric acid, it acts in the 
same way as all hydrazones, and phenyl hydrazine is eliminated ; the 
original unchanged sugar is not formed again, but an oxidation product 
of it is obtained, a so-called "Osone." In the example selected, the 
osone is : 

CH 2 . OH . (CH . OH) 3 . CO . CHO. 

If this compound is treated with a reducing agent, the aldehyde 
group and not the ketone group is reduced, and the original sugar is 
not obtained : 

CH 2 .OH(CH.OH) 3 .CO.CH 2 .OH. 

The aldose is converted into a ketose, the grape sugar into fruit 
sugar. The general importance of the reaction as applied to the sugars 
may be inferred from these brief statements. 

Experiment : A cold solution of 2 grammes of phenyl hydrazine 
hydrochloride and 3 grammes of crystallised sodium acetate in 
15 c.c. of water is treated with a solution of 1 gramme of pure 
grape sugar in 5 c.c. of water, and warmed on the water-bath. 
After about 10 minutes, the fine, yellow needles of the osazone 
begin to separate out; the quantity is increased by a longer 
heating. After heating an hour, the crystals are filtered off, 
washed with water, and allowed io dry in the air. Melting-point, 
205 . 

Phenyl hydrazine undergoes condensation with /?-diketones and 
/?-ketone-acid-esters with the formation of ring compounds contain- 
ing nitrogen — the so-called pyrazoles and pyrazolones. The phenyl 
methyl pyrazolone formed from acetacetic ester and phenyl hydrazine 
is of importance : 



.CH 2 .CO|OC 2 H 5 l = CH 3 - C - CH 2 .CO + H„0 + C 2 H 5 OH 

+ 1 ; II I 

N NH.C 6 H S N NC C H 5 



from which, by the action of methyl iodide, the important febrifuge 
" Antipyrine " — dimethyl phenyl pyrazolone is obtained : 



I I 

N N— C fi H : 



Antipyrine 



AROMATIC SERIES 



229 



If the primary hydrazines are boiled with copper sulphate, 1 or ferric 
chloride, 2 the hydrazine radical is replaced by hydrogen, and there is 
obtained, e.g., from phenyl hydrazine, benzene : 

C 6 H S . NH . NH 2 + 2 CuO = C 6 H + N 2 + H 2 + Cu 2 0, 
or C c H 5 .NH.NH 2 + CuO = C 6 H + N 2 + H 2 + Cu. 

The statements made above concerning the replacement of a diazo- 
group by hydrogen are also applicable to this reaction. If it is desired 
to prepare an amido-compound from an amido-free compound, and if 
the direct reduction of the diazo-compound by sodium stannous oxide 
or alcohol (see page 210) has been shown to be impracticable, then, as 
above, the hydrochloric acid salt of the corresponding hydrazine is pre- 
pared, the free hydrazine is liberated, and oxidised with caustic soda. 
The amido-free substance is not always easily volatile, as in the example 
cited. In a case of this kind, the oxidation may be effected in an open 
vessel ; the reaction product is obtained either by filtering or by extract- 
ing with ether. It may be pointed out here that it is more convenient to 
separate the hydrazine from the hydrochloric acid salt, and subject this 
to oxidation. If a hydrochloric acid salt of a hydrazine is oxidised, it 
may happen that the hydrazine radical will be replaced by chlorine : 

C 6 H 5 . NH . NH 2 , HC1 + 2 = C H 5 . CI + N 2 + 2 H 2 0, 

which may give rise to complications. 

12. REACTION: (a) PREPARATION OF AN AZO DYE FROM A DIAZO- 
COMPOUND AND AN AMINE, {b) REDUCTION OF THE AZO-COM- 
POUND 

Examples : (a) Helianthine from Diazotised Sulphanilic Acid and 
Dimethyl Aniline 
(b) Reduction of Helianthine 

{a) Dissolve 10 grammes of sulphanilic acid, dried on the 
water-bath, in a solution of 3.5 grammes of dehydrated sodium 
carbonate in 150 c.c. of water, and treat with a solution of 4.2 
grammes of pure sodium nitrite in 20 c.c. of water. To this 
mixture, after being cooled by water, is added a quantity of 
hydrochloric acid solution corresponding to 2.5 grammes of an- 



1 B. 18, 90. 2 B. 18, 



230 



SPECIAL PART 



hydrous hydrochloric acid. For this purpose, concentrated hydro- 
chloric acid is diluted with an equal volume of water, and the 
specific gravity of the dilute acid is determined by a hydrometer. 
Consult a table, to find the amount of anhydrous hydrochloric 
acid corresponding to the reading of the hydrometer. (See 
Graham-Otto, Vol. II. p. 318.) x 

Before diazotising the sulphanilic acid, a solution of 7 grammes 
of dimethyl aniline in the theoretical amount of hydrochloric acid 
is prepared. Aromatic bases cannot be neutralised with hydro- 
chloric acid in the same way as caustic potash, caustic soda, 
and ammonium hydroxide, by gradually treating with the acid and 
testing with blue litmus-paper until the liquid is just acid. In con- 
sequence of the weak basic character of the amines, their hydro- 
chlorides still give an acid reaction with blue litmus-paper, there- 
fore an acid reaction can be obtained even at the beginning of 
the neutralisation. Red fuchsine-paper possesses the property of 
becoming decolourised by free hydrochloric acid, which converts 
the red monoacid fuchsine into a colourless polyacid salt. The 
hydrochloric acid salts of bases, on the contrary, do not produce 
this decolourisation. In order to neutralise the dimethyl aniline 
(7 grammes), it is treated with 25 c.c. of water, and, with stirring, 
small quantities of concentrated hydrochloric acid are added ; 
after each addition a test is made to show whether or not the 
fuchsine-paper is decolourised. 

The dimethyl aniline hydrochloride thus obtained is added to 
the diazo-solution, and the mixture is made distinctly alkaline by 
the addition of not too much caustic soda solution. The dye 
separates out directly; the quantity can be increased if 25 
grammes of finely pulverised sodium chloride are added to the 
solution. After filtering off and pressing out on a porous plate, 
the dye is recrystallised from a little water. 

1 If the specific gravity of the hydrochloric acid has been determined, the per- 
centage of free anhydrous acid may be found without a table, by the following 
calculation : The decimal number is multiplied by 2, and a decimal point placed 
after the first two figures thus obtained, e.g., sp. gr. = 1.134; 2X134=268. 
Percentage contents = 26.8. If the sp. gr. is greater than 1.18, a table must be 
consulted. 



AROMATIC SERIES 23 I 

Preparation of Fuchsine- Paper : A crystal of fuchsine, the size 
of a lentil, is pulverised, dissolved by heating in 100 c.c. of water, 
and the solution filtered. 

Into this immerse strips of filter-paper 2 cm. wide ; they are 
dried either by suspending from a string in an acid-free place, 
or on the water-bath. The paper must not be an intense red, 
but only a faint rose colour. If the colour is too intense, the 
fuchsine solution must be correspondingly diluted with water. 

Instead of the fuchsine-paper, the commercial Congo-paper will 
serve, the red colour of which is changed to blue by free acid. 

(b) Dissolve 2 grammes of the dye in the least possible amount 
of water by heating ; while the solution is still hot, treat with a 
solution of 8 grammes of stannous chloride in 20 grammes of 
hydrochloric acid until decolourisation takes place. The colour- 
less solution is then well cooled, upon which, especially if the 
sides of the vessel are rubbed with a glass rod, sulphanilic acid 
separates out : it is filtered off through asbestos or glass-wool. 
The filtrate is diluted with water, and caustic soda solution is 
added until the oxyhydrate of tin separating out at first is again 
dissolved. It is then extracted with ether several times, the 
ethereal solution dried with potash, and the ether evaporated, 
upon which the p-amidodimethyi aniline remains as an oil : on 
cooling and rubbing with a glass rod, it solidifies. 

Reactions of p-Amido dimethyl Aniline : x The amidodimethyl 
aniline is treated gradually with small quantities of dilute sul- 
phuric acid until it is just dissolved. Add a few drops of this 
solution to a dilute solution of hydrogen sulphide in a beaker 
which has been treated with J^ of its volume of concentrated 
hydrochloric acid. To this mixture now add several drops of a 
dilute solution of ferric chloride. An intensely blue colouration, 
due to the formation of methylene blue, takes place. 

Diazo-compounds react with amines, as well as phenols, to form the 
Azo dyes : 2 



1 B. 16, 2235. 2 A. 137, 60; B. 3, 233. 



232 SPECIAL PART 

(i) C 6 H 5 .N 2 .C1 + C 6 H 5 .N(CH 3 ) 2 

= C 6 H 5 . N=N . C 6 H 4 . N(CH 3 ) 2 + HC1 

Dimethylamidoazo benzene 

(2) C 6 H 5 . N 2 . CI + C 6 H 5 . OH = C 6 H 5 . N=N . C 6 H 4 . OH + HC1 

(In presence of alkali) Oxyazo benzene 

In accordance with the earlier views concerning the structure of the 
diazo-compounds, the generation of the azo-compounds may be readily 
formulated by assuming that the acid radical of the diazo-compound 
combines with a benzene hydrogen atom to form an acid, and the 
resulting residues unite, e.g. : 

q 6 H 5 . N=N . [ Cl + Hl . C 6 H 4 . OH = C e H 5 . N=N . C 6 H 4 . OH + HC1 

This reaction is not so easily explained by the new diazonium formulae. 
In accordance with these two typical reactions, the vast number of 
monoazo dyes are prepared. The great number of possible combina- 
tions can be inferred from the following considerations : In reaction 
(i), instead of diazotised aniline, other bases, like o-toluidine, p-tolui- 
dine, xylidine, cuminidine, a-naphthyl amine, /3-naphthyl amine, etc., 
may be used. In addition, the most varied derivatives of these bases, 
especially their sulphonic acids, like sulphanilic acid, metanilic acid, 
the large number of a- and /3-naphthyl amines mono- to poly-sulphonic 
acids, may also be employed. Instead of dimethyl aniline, the diazo- 
compound can be combined or "coupled 11 with other tertiary, and in 
part also with secondary and primary amines, like diphenyl amine, or 
m-diamines, etc. In the second reaction, the diazo-compounds of the 
just mentioned bases can be employed as the starting-point, and these 
can be combined with mon-acid phenols, like cresol, naphthols, or di- 
acid phenols like resorcinol, or the sulphonic acids of these phenols, 
especially the numerous sulphonic acids of both naphthols. Since a dye 
must be soluble in water, and the alkali salts of the sulphonic acids of the 
dyes are more easily soluble than the mother substance containing no 
sulphonic acid groups, therefore, in the preparation of the azo dyes, the 
starting-point is usually a sulphonic acid. A few examples will explain 
these statements : 

I. Amidoazo Dyes 
/S0 3 H 
p-C 6 H 4 < .C 6 H 4 .N(CHo) 2 = Helianthine, 

Diazotised sulphanilic acid + dimethyl aniline 

/SOoH 
m-QH/ . C 6 H 4 .NH . C e H 5 = Metanilic Yellow, 

\N=N 

Diazot. Metanilic acid + diphenylamine 

/NH, 
C 6 H 5 . NzzN . C 6 H 3 < ' = Chrysoidine. 

\NH, 

Diazot. Aniline + m-phenylenediamine 



AROMATIC SERIES 233 

II. Oxyazo Dyes 

/SO3H 
p-C 6 H 4 < . C 10 H 6 . OH = Orange II., 

\N— N 

Diazot. Sulphanilic acid + /3-naphthol 

/S0 3 H 
C 10 H 6 < . C 10 H 6 . OH = Fast Red (first red azo dye), 

XNzzN 

Diazot. a-Naphthionic acid + 0-naphthol 

/OH 
C 6 H 5 . NzzN . C 10 H 5 <^ = Croceine Orange, 

Diazot. Aniline + croce'me acid 
(j8-Naphthol sulphonic acid) 

/OH 
(CH 3 ) 2 .C 6 H 3 .N=N.C 10 H/ = Xylidine Ponceau. 

\(S0 3 H) 2 

Diazot. Xylidine + /3-naphthol disulphonic acid 

Concerning the constitution of the azo dyes, provided the com- 
ponents are known, the only question to solve is : which hydrogen 
atom of the undiazotised component combines with the acid radical of 
the diazo-compound (the acid thus formed being eliminated). The 
question may be answered by investigating the reduction products of 
the azo dyes. By energetic reduction, best in acid solution with stan- 
nous chloride, the double NzzzN union is broken up, thus forming, with 
the addition of 4 atoms of hydrogen, two molecules of a primary 
amine, e.g. : 

/SO3H /S0 3 H /NH 2 

C 6 H 4 < .C 6 H 4 .N(CH 3 ) 2 +2H 2 =C 6 H 4 < +C 6 H 4 < 

\N=N \NH 2 \N(CH 3 ) 2 

From this equation it is evident that by reduction, the amine which 
was diazotised — in the above case sulphanilic acid — may be obtained 
again on the one hand, on the other an amido-group is introduced into 
the second component. If the constitution of this second product can 
be determined, then the constitution of the azo dyes is also determined. 
It may be stated as a general rule that, when a diazo-compound com- 
bines with an amine or phenol, the hydrogen atom in the para position 
to the amido- or hydroxyl-group is always substituted. In accordance 
with this, in the above case, p-amidodimethyl aniline ought to be 
obtained on reduction. If the para position is already occupied, then 
the o-hydrogen atom unites with the acid radical. 



234 SPECIAL PART 

In some cases, the formation and consequent reduction of an azo 
dye with the introduction of an amido-group into a phenol or amine is 
of practical value. 

Azo dyes which contain two " chromophore groups," NzzzN, and 
which are called dis- or tetr-azo dyes, can be prepared ; two methods 
may be employed: (i) The starting-point is an amido-azo-compound 
which already contains one azo group ; this is diazotised, and then 
united with an amine or phenol. " Biebrich scarlet " is obtained in 
this way, by diazotising the disulphonic acid of amidoazobenzene, and 
combining it with /3-naphthol : 

.S0 3 H /S0 3 H 

\N=N \N=zN 



Diazot. Amidoazobenzene disulphonic acid + /3-naphthol 

(2) A diamine is the starting-point ; this is diazotised, and the bisdiazo- 
compound is combined with two molecules of an amine or phenol. 
To this class belong the important dyes of the Congo group, prepared 
from the benzidine bases (see page 204), e.g. : 

7 NH 2 
C 6 H-N=N-C 10 H 5 <( 
I \SO s H rrtrwy „ 

7 NH 2 = Con S > 
C 6 H-N=N-C 10 H 5 < 
. T \SOoH 

Diazot. Benzidine + 2 mol. a-naphthionic acid 

,OH 



C 6 H 4 .N=N.C C H 3N 

CO. OH 

qtj = Chrysamine. 

c 6 h 4 .n=n.c 6 h/ 

•> , - XX). OH 

Diazot. Benzidine + 2 mol. salicylic acid 

These Congo dyes possess the noteworthy property of colouring 
vegetable fibres (cotton) directly, whereas, with all other azo dyes, the 
cotton must be mordanted before dyeing. 

In conclusion, the above dye-stuff reaction (which may be used for 
detecting the smallest amount of hydrogen sulphide) is technically 
carried out on the large scale, for the manufacture of the important 
methylene blue. The reaction takes place as follows : From two mole- 
cules of the diamine there is split off on oxidation with ferric chloride, 



AROMATIC SERIES 



235 



one molecule of ammonia, while a derivative of diphenyl amine is 

formed : 

/NCCHgX, /NCCH3), 



C 6 H 4 



= NH 

,NH[H 

C 6 H 4 C G H 4 

\n(CH 3 ) 2 X N(CH 3 ) 2 



+ NH 3 



In the presence of hydrogen sulphide and hydrochloric acid, there 
is formed from this, by the oxidising action of ferric chloride, a deriva- 
tive of thiodiphenylamine, as follows : 



/N(CH 3 ) 2 

/ C 6 H 3\ 

= 3 H 2 + N< >S 



/NCCH3), 






C 6 H 3 

1 


H 

H 


/ 


+ 


N H +. 


S 


1 
C 6 H 3 


H 
H 


' + ol 


NnT( 

+ 


CH 3 ) 2 . 



H 


CI 



XX N(CH 3 ) 2 C1 

Methylene blue 



13. REACTION: PREPARATION OF A DIAZOAMIDO-COMPOUND 

Examples : Diazoamidobenzene from Diazobenzenechloride and 

Aniline l 



Dissolve 10 grammes of freshly distilled aniline in a mixture 
of 100 c.c. of water, and that quantity of concentrated hydro- 
chloric acid corresponding to 1 2 grammes anhydrous hydrochloric 
acid (determine the sp. gr. by a hydrometer). The solution is 
cooled with ice-water, and diazotised with a solution of 8 grammes 
of sodium nitrite in 50 c.c. of water, in the manner already de- 
scribed. A solution of 10 grammes of aniline in 50 grammes of 
water is previously prepared according to the directions already 
given, and exactly the theoretical amount of hydrochloric acid, 2 



1 A. I2i, 257. 



2 See page 230. 



236 SPECIAL PART 

after it has been well cooled with ice-water, is added to the 
diazo-solution, with stirring. Further, 50 grammes of sodium 
acetate are dissolved in the least possible amount of water, the 
cooled solution is added, with stirring, to the mixture of the diazo- 
compound with aniline hydrochloride. After standing half an 
hour, the diazoamidobenzene separates out, and is filtered off with 
suction, washed several times with water, well pressed out on a 
porous plate, and recrystallised from ligroin. Melting-point, 98 . 
Yield, almost theoretical. 

If one molecule of a diazo-compound is allowed to act on one mole- 
cule of a primary amine, the acid radical of the former unites with the 
hydrogen atom of the latter, upon which the organic residues combine, 
as in the formation of the azo dyes. In this case, an amido-hydrogen 
atom is eliminated, so that a compound containing a chain of three 
nitrogen atoms -is formed; in the formation of an azo dye, one of the 
benzene-hydrogen atoms of the amine is eliminated : 

C 6 H 5 .N 2 .C1 + C 6 H 5 .NH 2 = C 6 H 5 .N=N.NH.C ( .H 5 + HC1 

Diazoamidobenzene 

Mixed diazo-compounds may also be prepared by causing the diazo- 
derivative of an amine to combine with another amine : 

/CH 3 
C 6 H 5 . N 2 . CI + C 6 H 4 < = C 6 H 5 . N=N . NH . C 6 H 4 . CH 3 + HC1 

\NH 2 

Benzenediazoamidotoluene 

Diazo-compounds combine only with the free amines to form diazo- 
amido compounds ; the object of the addition of sodium acetate at the 
end of the reaction (see above) is to set free the base from aniline 
hydrochloride. 

The diazoamido-compounds are yellow substances which do not dis- 
solve in acids. They are far more stable than the diazo-compounds, 
and may be recrystallised without decomposition. Still, if they are 
heated rapidly they puff up suddenly and decompose. In their reac- 
tions they behave like a mixture of a diazo-compound and an amine. 
If, e.g., they are boiled with hydrochloric acid, they decompose with 
evolution of nitrogen, and form a phenol and an amine : 

C 6 H 5 .N=N.NHX 6 H 3 + H 2 = C 6 H 5 .OH = C 6 H 5 .NH 2 + N 2 



AROMATIC SERIES 237 

On heating with cuprous chloride and hydrochloric acid, the Sand- 
meyer reaction takes place : 

C 6 H 5 . N=N . NH . C 6 H 3 + HC1 = C 6 H 5 . CI + C 6 H 5 . NH 2 + N 2 

By reduction with acetic acid and zinc dust, they form a hydrazine : 

C 6 H 5 .N=N.NH.C 6 H 5 + 2 H 2 = C 6 H 5 .NH.NH 2 + C 6 H 5 .NH 2 

But, in addition to the reaction-product of the diazo-radical, there is 
always formed one molecule of an amine. 

Under the influence of nitrous acid, they decompose, the amine 
residue being diazotised, into two molecules of a diazo-compound : 

C 6 H 5 . N=N . NH . C 6 H 5 + HN0 2 + 2 HC1 = 2 C 6 H 5 . N 2 . CI + 2 H 2 

If a diazoamido-compound is warmed with an amine in the presence 
of some amine hydrochloride, transformation to the isomeric amidoazo- 
compound takes place : 

C 6 H 5 . N=N . NH . C 6 H 5 = C G H 5 . N — N . C<;H 4 . NH 2 

Amidoazobenzene 

The next preparation deals with this reaction. 

The diazo-compounds also have the power of combining with sec- 
ondary amines to form diazoamido-compounds, — the combinations 
with an alkaloid base, piperidine C 5 H U N : 

CH 2 

H 9 C| |CH( 




L 2 

NH 
are of especial value for preparations. If they are gradually warmed 
with hydrofluoric acid, they are decomposed with the evolution of nitro- 
gen into piperidine and a fluoride : 2 

C 6 H 5 . N=N .N .C 5 H 10 + HF1 = C 6 H 5 . Fl + C 5 H n N + N 2 

Benzenediazopiperidine Fluorbenzene 

In this way it has been possible to prepare the aromatic fluorides. 

In accordance with the older views it was believed that the aromatic 
fluorides could not be obtained from the diazo-compounds in the same 
way in which the analogous chlorides, bromides, and iodides are pre- 
pared ; recently however they have been obtained by the direct decom- 
position of the diazo-fluorides. 



1 A. 243, 239. 



238 SPECIAL PART 



14. REACTION: THE MOLECULAR TRANSFORMATION OF A DIAZO- 
AMIDO-COMPOUND INTO AN AMIDOAZO-COMPOUND 

Example : Amidoazobenzene from Diazoamidobenzene 

To a mixture of 10 grammes of crystallised diazoamidobenzene, 
finely pulverised, and 5 grammes of pulverised aniline hydro- 
chloride, contained in a small beaker, add 25 grammes of freshly 
distilled aniline ; the mixture is then heated, with frequent stirring, 
one hour, on the water-bath, at 45 . It is then transferred to a 
larger vessel, and treated with water ; dilute acetic acid is added, 
until all the aniline has passed into solution, and the undissolved 
precipitate remaining is completely solid. This is filtered off, 
washed with water, heated in a large dish with a large quantity 
of water (about a litre), and gradually treated with hydrochloric 
acid until the greatest portion of the precipitate is dissolved. 
From the filtered solution, steel-blue crystals of amidoazobenzene 
separate out, on long standing ; these are filtered off, and washed 
with dilute hydrochloric acid, not with water. 

If aniline hydrochloride is not at hand, prepare it by adding 
aniline to concentrated hydrochloric acid, with stirring. After 
cooling, the pasty mass of crystals separating out is filtered on 
glass-wool, pressed firmly together on the filter with a pestle, and 
then spread in thin layers on a porous plate. 

In order to obtain the free amidoazobenzene, the hydrochloride 
is warmed with dilute ammonia, the free base filtered off, dis- 
solved in alcohol by heating, and hot water is added until the liquid 
begins to be turbid. Melting-point, 127-12 8°. Yield, 6-8 grammes. 

If a diazoamido-compound is heated with an amine and some amine 
hydrochloride, it goes over to an amidoazo-compound. The most 
probable cause of the reaction is that the amine residue of the diazo- 
amido-compound unites with a benzene-hydrogen atom of the amine 
hydrochloride, upon which the diazo-residue unites with the residue 
of the amine salt to form amidoazobenzene : 



CTT . N — N . j NH . C.H, + H ■ . C.H, . NH, 



'6 iA 5 



= C e H 5 _.N-=N.C 6 H 4 .NHj 

Amidoazobenzene 



AROMATIC SERIES 239 

While the amidoazobenzene does not unite with hydrochloric acid, 
the new molecule of the amine formed in the reaction does, and thus 
there is a molecule of the amine hydrochloride present, which again 
causes the transformation, so that a small amount of the hydrochloride 
may transform an indefinitely large amount of the diazoamido-compound. 

If amidoazobenzene is reduced, p-phenylene diamine and aniline are 
obtained. The transformation accordingly results in the formation of 
a compound in which the amido-groups are in the para position, which 
always happens when the para position is unoccupied. The amidoazo- 
compounds possess weakly basic properties ; but if their salts are 
treated with much water, they partially dissociate. 

The amidoazobenzene hydrochloride came into the market formerly, 
as a yellow dye, under the name of "Aniline Yellow.'" At present, it 
is scarcely used, but there is prepared from it, by heating with sulphuric 
acid, a mono- or di-sulphonic acid, which in the form of its alkali salts 
finds application as a dye under the name of " Acid Yellow, 1 ' or " Fast 
Yellow.' 1 As already mentioned under the dis-azo dyes, from the 
diazo-compound of this dye, " Biebrich Scarlet " may be made by com- 
bination with /3-naphthol. Finally, the amidoazobenzene is still used 
for the preparation of the Induline dyes. 



15. REACTION: OXIDATION OF AN AMINE TO A QUINONE 
Example : Quinone from Aniline * 

To a solution of 25 grammes of aniline in a mixture of 200 
grammes of concentrated pure sulphuric acid and 600 c.c. of water 
contained in a thick-walled beaker (a small battery jar), cooled 
to 5 by being surrounded with ice, add gradually, with constant 
stirring (use a small motor), from a dropping funnel, a solution of 
25 grammes of sodium dichromate in 100 c.c. of water (Fig. 69). 
Should the temperature rise above io°, the addition of the dichro- 
mate must be discontinued for a short time and a few pieces of ice 
thrown into the beaker. The reaction-mixture is then allowed to 
stand over night in a cool place, and the next morning it is again 
cooled and stirred, while a solution of 50 grammes of sodium di- 
chromate in 200 c.c. of water is added. After the mixture has been 
allowed to stand until midday, it is divided into two equal parts, one 
of which is worked up into quinone as follows : In a large separating 

1 A. 27, 268; 45, 354; 215, 125; B. 19, 1467; 20, 2283. 



240 



SPECIAL PART 



funnel one half is treated with § its volume of ether, and the two 
layers thus formed are carefully shaken together. If the shaking 
is too vigorous, the layers will not readily separate. After allowing 
it to stand for half an hour, the lower layer is run off (see page 
44, Separation of coloured liquids), the ethereal solution is filtered 
through a folded filter, and the ether distilled off (water-bath with 
warm water). The water solution is again extracted with the con- 
densed ether, and the ether again distilled from the same flask as 
before. In order to obtain perfectly pure quinone, a rapid current 
of steam is passed over the crude product — it is not treated with 




Fig. 69. 
water ; the pure quinone is carried over with the steam to the 
condenser and receiver, where it crystallises in the form of golden- 
yellow needles ; they are filtered off and dried in a desiccator. 
Melting-point, 116 . Yield, 10-12 grammes. 

If sodium dichromate is not at hand, the potassium salt may be 
used for the oxidation. In this case, 25 grammes of aniline are 
dissolved in a mixture of 200 grammes of sulphuric acid and 800 
c.c. of water ; then add, as above, with stirring and good cooling, 
25 grammes of potassium dichromate, powdered extremely fine. 
On the next day add 50 grammes of this salt. In other respects, 
proceed as above. 

Many primary aromatic amines yield quinones on oxidation with 
chromic acid. But the reaction cannot be expressed in a simple equa- 
tion ; still, it is always true that the amido-group and the hydrogen 



AROMATIC SERIES 24 1 

atom in the para position to this are each replaced by an oxygen 
atom, e.g.: 

C C H 5 . NH 2 — ■>- C 6 H 4 2 

Quinone 

o-C 6 H 4 < ->- C H 3 / 

\NH 2 ^0 2 

Toluidine Tolyl quinone 

The tendency to form quinones is so great that even in cases where the 
para position to the amido-group is occupied by an alkyl (methyl) radical, 
the latter is split off and a quinone (poorer in carbon contents) is formed. 
Indeed, in the simplest cases, like p-toluidine and asym. m-xylidine, the 
reaction is very incomplete ; however, mesidine, as well as pseudocumidine, 
give satisfactory yields of quinones belonging to the next lower series : 

NH 9 





Pseudocumidine 



But if the "para position is occupied by an amido-, oxy-, or sulphonic 
acid-group, this is eliminated and a quinone formed : 

/NH 2 
p-C c H/ 

X NH 2 . 

7 NH 9 X 
p-C 6 H 4 < " — ^ C 6 H 4 O a 



7 NH, / 
p-C 6 H 4 <( 

x SO,,H 

From these methods of formation it follows that the two quinone- 
oxygen atoms are in the para position to each other. The quinone 
reaction can be used in doubtful cases to decide whether a compound 

R 



242 



SPECIAL PART 



belongs to the para series. The quinones can also be obtained very 
easily from p-dioxy-compounds as well as from the p-sulphonic acids 
of mon-acid phenols : 

/OH 
p-C 6 H 4 < + O = C 6 H 4 2 + H 2 



p-C 6 H 4 < 



OH 
OH 



C G H 4 2 . 



Two formulae for the quinones have been proposed — the Peroxide- 
and Ketone-formula : 

O 



HC 



C 



CH 



HCv JCP 



-O 




c 

hc/ x:h 



hcv ;ct 
c 



o 

Ketone formulae 



Peroxide formulse 

According to the former the quinones still contain the true benzene 
ring with either three double or six centric bonds. The two oxygen 
atoms are only singly united with the benzene-carbon atoms, and are 
united to each other as in the peroxides. According to the second 
formula, the quinones do not contain the true benzene ring, but they 
are derived from a dihydrobenzene, 

H H 

c 
hc/\:h 



HCv XH 
C 



H H 

and are regarded as the di-ketone derivative of this. According to 
this conception, the oxygen atoms are connected by two bonds, as in 
the ketones, with the carbon atoms of the benzene nucleus. The facts 
in favour of the first formula are these : In many reactions both of the 



AROMATIC SERIES 243 

oxygen atoms are replaced by two univalent atoms or radicals. Thus, 
e.g., by the action of phosphorus pentachloride on quinone, p-dichlor- 
benzene is formed, while the second formula would lead one to expect 
a tetra-chloride. In support of the second formula is the fact that 
hydroxylamine acts directly on quinones, as on ketones, with the 
formation of a mono- or di-oxime. 

The quinones are yellow compounds, possessing a characteristic 
odour ; they are easily volatile with steam, but with a slight decomposi- 
tion. They are somewhat volatile even with the vapour of ether, as 
one observes in the preparation of quinone. On reduction they take 
up two hydrogen atoms and pass over to hydroquinones. (See the 
next preparation) e.g. : qtt 

C 6 H 4 2 + H 2 = C 6 H 4 < 



^OH 

Hydroquinone 



16. REACTION: REDUCTION OF A QUINONE TO A HYDROQUINONE 
Example : Hydroquinone from Quinone 

Conduct sulphur dioxide into the second half of the quinone 
solution obtained above, until the liquid smells intensely of the 
gas, then allow it to stand for 1-2 hours. Should the odour of 
sulphur dioxide vanish, it is passed in again and the mixture 
allowed to stand for some time as before. It is then extracted 
with the ether distilled from the quinone in the preceding experi- 
ment, several times ; the ether is evaporated or distilled, and the 
hydroquinone, well pressed out on a porous plate, is crystallised 
with the use of animal charcoal from a little water. Melting-point, 
169 . Yield, 8-10 grammes. 

Since the hydroquinone solution may be extracted with ether 
with much greater ease than the quinone solution, and since the 
hydroquinone is smoothly oxidised to quinone, the preparation of 
quinone may be done as follows : The entire qtiantity of the oxi- 
dation product is saturated with sulphur dioxide, and as just de- 
scribed the hydroquinone may be obtained by repeated extraction 
with ether. In order to convert it into quinone it is dissolved in the 
least possible amount of water, to which is added 2 parts of con- 
centrated sulphuric acid to 1 part of hydroquinone ; the well- 



244 



SPECIAL PART 



cooled liquid is treated with a water solution of sodium dichro- 
mate until the green crystals of quinhydrone (an intermediate 
product between quinone and hydroquinone) separating out' in 
the beginning have changed into pure yellow quinone. 

The equation for the formation of hydroquinone from quinone has 
been given above. All homologous quinones react in the same way. 
The hydroquinones are di-acid phenols, which dissolve in alkalies and 
show all the properties of phenols. They are not volatile with steam. 



17. REACTION: BROMINATION OF AN AROMATIC COMPOUND 

Example : Mono- and Di-brombenzene from Bromine and Benzene 

A wide-neck 250 c.c. flask is connected with a vertical tube 
50 cm. long and i|- cm. wide, the upper end of which is closed by 
a cork bearing a glass tube, not too narrow, bent twice at right 
angles. The other end is connected with a flask containing 
250 c.c. of water, by a cork having a small canal in the side 
(Fig. 70). The tube does not touch the 
liquid, but the end is about 1 cm. above the 
surface. After 50 grammes of benzene and 
1 gramme of coarse iron filings (the bromine 
carrier) have been placed in the flask, it is 
cooled in a large vessel (battery jar) filled 
with ice-water; through the vertical tube 
there is added 40 c.c. = 120 grammes of 
bromine : the narrow tube is immediately 
connected with the vertical tube. After 
some time an extremely energetic reaction 
will begin, generally spontaneously, with the 
evolution of hydrobromic acid, which is 
completely absorbed by the water. Should 
the reaction not begin at once, the ice-water 
is removed for a short time, and if necessary 
the flask is immersed for a moment in 
slightly warm water. But as soon as even a 
weak gas evolution begins, the flask is at once cooled again, since 




AROMATIC SERIES 245 

otherwise the reaction easily becomes too violent. Should this 
happen in spite of the cooling, the cause is found in the fact that 
the iron filings used were too fine. In other experiments use 
coarser filings or small iron nails. When the main reaction is 
over, the ice-water is removed, the flask dried and heated over a 
small flame until the red bromine vapours are no longer visible 
above the dark-coloured liquid. The reaction-product is washed 
several times with water and then distilled with steam. As soon 
as crystals of dibrombenzene separate out in the condenser, the 
receiver is changed and the distillation continued until all the di- 
brombenzene has passed over. The liquid monobrombenzene is 
separated from the water, dried with calcium chloride, and sub- 
jected to a fractional distillation ; the portion passing over between 
140-170 is collected separately. This is again distilled, and the 
portion going over between 150-160 collected. The boiling-point 
of the pure monobrombenzene is 15 5 . Yield, 60-70 grammes. 
The residue boiling above 170 remaining in the flask after the 
two distillations, is poured, while still warm, on a watch-glass, and 
after cooling is pressed out, together with the separately collected 
dibrombenzene, on a porous plate. On crystallising from alcohol, 
coarse colourless crystals of p-dibrombenzene are obtained, which 
melt at 89 . 

The by-product, hydrobromic acid, is purified as described in 
the Inorganic Part. (See page 345.) 

A portion of the hydrogen of the aromatic hydrocarbons is very 
easily replaced by bromine, especially in the presence of a carrier, even 
at low temperatures ; while in the aliphatic series the direct substitution 
of bromine is not used as a preparation method for alkyl bromides, 
the aromatic bromides are readily prepared in this way. According 
to the amount of bromine used one or more hydrogen atoms may be 
substituted; it may happen, e.g., particularly with benzene under the 
influence of an energetic bromination, that all the hydrogen atoms may 
be replaced by bromine. A single bromide, even on using only the 
theoretical amount of bromine, is never formed ; but rather a portion 
of the hydrocarbon is brominated short of the theoretical action, and 
another portion is always acted upon farther, with the formation of a 
higher bromine substitution product. Thus in the example above cited, 
besides the principal product, monobrombenzene, a small quantity of 
dibrombenzene is formed : 

C 6 H 6 + Br, = C H 5 Br + HBr 
C C H + 2 Br. 2 = C 6 H 4 Br 2 + 2 HBr 



246 SPECIAL PART 

In most cases, however, the principal product may be separated 
from the by-product without difficulty by distillation or crystallisation. 
Since the hydrogen atoms substituted by bromine combine with bromine 
to form hydrobromic acid, therefore, for the introduction of each 
bromine atom, a molecule (two atoms of bromine) must be used. 

The introduction of bromine can be essentially facilitated by the use 
of a so-called bromine carrier. As such, the bromides of metalloids, 
or metals, are used; (1) either in the already prepared condition, or 
(2) they can be generated from their elements in the reaction. To 
the first class belong ferric bromide and aluminium bromide. The 
action of ferric bromide depends on the fact that on being reduced to 
ferrous bromide, it yields bromine in statu nascendi: 

FeBr 3 = FeBr 2 + Br. 

Ferric bromide Ferrous bromide 

Since the ferrous bromide unites with bromine again, to form ferric 
bromide, a small quantity of this has the power to transfer an indefi- 
nitely large quantity of bromine : 



Instead of ferric bromide, ferrous bromide or anhydrous ferric chloride 
may be used. The latter decomposes with hydrobromic acid to ferric 
bromide and hydrochloric acid : 

FeCl 3 + 3 HBr = FeBr 3 + 3 HC1. 

The activity of aluminium bromide is explained by the fact that it 
unites with the hydrocarbon to form a double compound which is more 
capable of reacting with other substances than the hydrocarbon itself. 

To the second class belong iodine, sulphur, phosphorus, iron, alumin- 
ium, etc. If these elements are added to the brominating mixture, 
the corresponding bromides are formed, e.g. : 

I + Br = IBr 1 . 

While these give up all their bromine, or a portion of it, as is the 
case with ferric bromide, in the atomic condition, the residue again 
unites with bromine, and as above, a small quantity of the carrier may 
transfer large quantities of atomic bromine. 

Bromine can also act on aromatic hydrocarbons to form addition 
products, since it may be added in one, two, or three molecules, and 
thus break up the double or centric union. Thus, e.g., the hexabrom- 



1 Compare page 141. 



AROMATIC SERIES 247 

addition product, C,H 6 Br G , is obtained from the action of bromine on 
benzene in the sunlight. Since the addition products render difficult 
the purification of substitution products, especially on distillation (they 
decompose when distilled), it is often necessary to remove them before 
the purification, by long boiling with alcoholic caustic potash, or alco- 
holic caustic soda. Under these conditions, one-half of the bromine 
atoms added in common with the same number of hydrogen atoms 
are abstracted as hydrobromic acid ; the residue of the molecule is 
converted into a substitution derivative, which is not troublesome in 
the purification : 

C 6 H 6 Br 6 = C G H 3 Br 3 + 3 HBr. 

On brominating benzene, the same products will be formed, whether 
the temperature is high or low, but when its homologues are treated 
with bromine, the nature of the products depends upon the temperature. 
As will be pointed out more fully, under the chlorination of toluene, 
the law holds here, that at low temperatures the bromine enters the 
ring ; at high temperatures, the side-chain, e.g. : 

/CH 3 

C G H 3 . CH, + Br., = C G H 4 < ' + HBr 
\Br 

Ordinary temperature Bromtoluene 

C 6 H. . CH ;i + Br 2 = C 6 H fl . CH 2 . Br + HBr. 

Boiling temperature Benzylbromide 

The aromatic bromides which contain bromine in the benzene 
nucleus are either colourless liquids or crystals, which in contrast with 
the side-chain substituted isomers in part possess an aromatic odour, 
and their vapours do not attack the eyes and nostrils. The bromine 
is held very firmly in them, more firmly than in the aliphatic bromides, 
and cannot be detected by silver nitrate. While the aliphatic bromides, 
as mentioned under bromethyl, decompose with ammonia, alcohol, 
alkalies, etc, to form amines, ethers, alcohols, etc., respectively, these 
reagents do not act on the aromatic bromides. The bromides contain- 
ing the bromine in the side-chain, behave like their aliphatic analogues. 

By the action of sodium amalgam, the bromine may be replaced by 
hydrogen, e.g. : 

C 6 H 5 . Br + H 2 = C 6 H 6 + HBr. 

From the 
amalgam 

The aromatic bromides are of synthetical importance, especially for 
the building up of homologous hydrocarbons and the preparation of 
carbonic acids : 



248 



SPECIAL PART 



C 6 H 5 .C 2 H 5 + 2NaBr 
C 6 H 5 . Br + Na 2 + C0 2 = C 6 H 5 . CO . ONa + NaBr. 

The next preparation will take up the first of these reactions in 
detail. 

The hydrocarbons and most of their derivatives, like nitro-, amido- 
compounds, aldehydes, acids, etc., may be brominated with greater or 
less ease. At this place, the various modifications by which the bromi- 
nation may be effected will be mentioned. If a substance is very 
easily brominated, the bromine may be used in a diluted condition. 
For this purpose, either bromine water or a mixture of bromine with 
carbon disulphide or glacial acetic acid may be employed. In many 
cases a bromination may be very well effected by using gaseous bro- 
mine. The method of procedure is as follows : 
The substance is spread out in thin layers on 
a watch-glass and placed under a glass bell-jar, 
under which is also a small dish containing 
bromine. If it is desired to cause bromine to 
act gradually, it is allowed to drop from a sepa- 
rating funnel, in concentrated form or in solu- 
tion, on the compound to be brominated. If 
an extremely slow and very careful bromination 
is desired, the bromine may be allowed to flow 
drop by drop from a siphon-shaped capillary 
tube. If bromination takes places with diffi- 
culty, the brominating mixture is heated ; either 
in an open vessel or in a sealed tube. In the 
first case the condensing apparatus cannot, as 
usual, be connected to the flask with a cork or 
rubber stopper, since this is soon attacked and 
destroyed by the bromine. Instead, the con- 
denser is well wrapped with asbestos twine 
and then pushed into the conical part of the 
neck of the flask, the asbestos being pressed in 
with a knife. A condenser of the kind repre- 
sented in Fig. 71 can also be used. A long 
tube c, sealed at one end, is closed by a two-hole 
cork, through one of which passes a long glass 
tube reaching almost to the bottom a ; the other bears a short tube just 
passing through the cork. Water is caused to flow through a ; it flows 




Fig. 71. 



AROMATIC SERIES 249 

out of b. This cooling apparatus is suspended in the heating-flask, 
which is selected with as long a neck as possible. 



18. REACTION: FITTIG'S SYNTHESIS OF A HYDROCARBON 
Example : Ethyl Benzene from Brombenzene and Bromethyl 1 

In a dry, round, i-litre flask, provided with a long reflux con- 
denser (the flask is supported on a straw ring in an empty water- 
bath), place 27 grammes of sodium, cut in scales as thin as 
possible with a sodium knife, and add 100 c.c. of alcohol-free, 
dry ether prepared as described below. As soon as this has 
been completely dried by the sodium, which may be recognised 
by the fact that the upper surface is no longer disturbed by wave- 
like motions (after several hours' standing), pour through the con- 
denser a mixture of 60 grammes of brombenzene and 60 grammes 
of bromethane, and allow to stand until the next day. Should the 
liquid begin to boil gently, which may easily happen at a summer 
temperature, cold water is poured into the water-bath. Water is 
not allowed to run through the condenser over night. During the 
reaction, the bright sodium will be changed to a blue powder, and 
an ethereal solution of ethylbenzene is formed. The ether is then 
distilled off on a water-bath, and the condenser is replaced with 
an air condenser 40-50 cm. long and 1 cm. wide, containing a 
short bend. After the flask has been placed in an oblique posi- 
tion, the extreme end of its neck is clamped loosely, and the 
ethylbenzene is distilled from the sodium bromide and sodium 
by a large, luminous fia??ie, which is kept in constant motion. 
With the use of a Linnemann apparatus, the crude product is 
finally subjected to two distillations. The boiling-point of pure 
ethylbenzene is 135 . Yield, about 25 grammes. 

The residue of sodium bromide and sodium remaining in the 
flask must be handled with extreme caution. Water must not be 
added to it, nor must it be thrown into the sink or waste-jars, nor 
allowed to stand a long time ; it is better to throw the flask, which 



1 A. 131, 303. 



250 SPECIAL PART 

cannot be used again, and its contents into some open place. The 
sodium residue may be rendered harmless by throwing water on it 
from a great distance. 



Preparation of Anhydrous, Alcohol-free Ether 

Shake 200 grammes of commercial ether in a separating fun- 
nel with half its volume of water ; the latter is allowed to run off, 
and the operation repeated a second time with a fresh quantity 
of water, by which the alcohol is removed. The ether is dried by 
standing over calcium chloride, not too little, two hours. It is 
then filtered through a folded filter, and can now be used for the 
above reaction. 

Fit-tig's synthesis of the aromatic hydrocarbons is the analogue of 
Wurtz 1 synthesis of the aliphatic hydrocarbons, e.g. : 

2 C 2 H 3 I + 2 Na = C 2 H 5 . C 2 H 5 + 2 Nal 

Ethyl iodide Butane 

C 6 H 5 . Br + C 2 H 5 Br + 2 Na = C B H 5 . C 2 H 5 + 2 NaBr. 

Ethylbenzene 

The bromides of the homologues of benzene react in a similar way, e.g. : 

/CH 3 /CH 3 

C 6 H 4 < + ICH. +. Na 2 = C 6 u/ + NaBr + Nal. 

\Br \CH 3 

Bromtoluene Xylene 

The three isomeric bromtoluenes do not react with the same ease. 
While the p-bromtoluene gives a good yield of p-xylene, the o-com- 
pound does not give good results, and the m-compound generally forms 
no xylene. Two alkyl residues can also, in many cases, be introduced 
into a hydrocarbon simultaneously, e.g. : 

/Br /CH 3 

p-C e H/ +2 ICH3 + 2 Na 2 = p-C 6 H/ + 2 NaBr + 2 Nal. 

>Br \CH 3 

The great number of hydrocarbons which may be prepared by Fittig's 
reaction is apparent from the above examples. The value of the reac- 
tion is still further increased by the fact that a halogen atom in the 
side-chain of an aromatic hydrocarbon also reacts in the same way. 



AROMATIC SERIES 25 I 

Though the halogen cannot be replaced by a methyl or ethyl radical, 
yet the reaction for the introduction of the higher alkyl residues is 
of great service, e.g. : 

C G H 5 .CH 2 C1 + CH 3 .CH 2 .CH,Br + Na 2 

Benzyl chloride Propyl bromide 

= C e H 5 . CH 2 . CH 2 . CH 2 . CH 3 + NaCl + NaBr. 

Butylbenzene 

Also by means of this reaction, two aromatic residues may be made 
to combine, and thus form the hydrocarbons of the diphenyl series, e.g. : 

2 C G H 5 . Br + Na 2 = C 6 H 5 . C 6 H 5 + 2 NaBr. 

Diphenyl 

Finally, the hydrocarbons of the dibenzyl series can also be prepared, 
e.g. : 

2 C 6 H 5 . CH 2 C1 + Na 2 = C 6 H 5 . CH 2 . CH 2 . C 6 H 5 + 2 NaCl. 

Dibenzyl 

In conducting operations involving the Fittig reaction, various 
modifications may be introduced, according to the ease with which the 
reaction takes place. If the reaction occurs at the ordinary temperature 
easily, then an indifferent diluent like ether, ligroin, carbon disulphide, 
or benzene is employed. These substances are not alike in their activity, 
since ligroin and benzene generally prolong the reaction, and on this 
account find application in a very energetic, reaction ; ether does not 
retard the reaction, but causes it to be more regular. At times, the 
reaction-mixture will not act, even on long standing. In this case, 
the reaction can frequently be started by a short heating, or the addi- 
tion of a few drops of ethyl acetate. Since the use of this compound, 
at times, causes a very stormy action, it is more advantageous to wait 
for the reaction to begin spontaneously, even if a long time is necessary. 
In syntheses which are moderately difficult, the reaction-mixture, treated 
with a diluent, can be heated on the water-bath or in an oil-bath ; 
while, if the reaction takes place with great difficulty, the mixture, 
generally without dilution, must be heated in an oil-bath. In the 
latter case, the reaction may be still further facilitated by heating under 
pressure of a mercury column. By this means, it is possible to heat 
the reacting substances in an open vessel above their boiling-points. 
(Fig. 72.) 




Fig. 72. 



AROMATIC SERIES 253 



19. REACTION: SULPHONATION OF AN AROMATIC HYDRO- 
CARBON (I) 

Example : (a) Benzenemonosulphonic Acid from Benzene and 
Sulphuric Acid 1 
(&) Sulphobenzide. Benzenesulphonchloride. Ben- 
zenesulphonamide 

(a) To 150 grammes of liquid fuming sulphuric acid, containing 
from 5-8 °lc of anhydride, placed in a 200 c.c. flask provided 
with an air condenser, gradually add, with good shaking and cool- 
ing with water, 40 grammes of benzene ; before the addition of a 
new portion, always wait until the last portion, which at first floats 
on the surface of the acid, dissolves on shaking. The sulphona- 
tion requires about 10-15 minutes. The reaction-mixture is then 
added, with stirring, drop by drop, from a separating funnel, to 
three to four times its volume of a cold, saturated solution of 
sodium chloride contained in a beaker. In order that the solution 
may not be heated above the room temperature, the beaker is 
placed in a large water-bath filled with ice-water. After some 
time, but with especial ease when the walls of the vessel are rubbed 
with a sharp-edged glass rod, the sodium salt of benzenesulphonic 
acid separates out in the form of leaflets of a fatty lustre ; the 
quantity is increased, on long standing, to such an extent that the 
beaker may be inverted without spilling its contents. If the sepa- 
ration of crystals does not begin, 10 c.c. of the liquid is shaken in 
a corked test-tube, and cooled by immersion in water. The solid- 
ified content of the tube is then added to the main quantity in 
the beaker. In summer, at times, it may require a several hours' 
standing before the separation of crystals is ended. The pasty 
mass of crystals is then filtered off with suction on a Buchner 
funnel, firmly pressed together with a pestle, and washed with a 
little saturated sodium chloride solution. 

To obtain the salt perfectly dry it is transferred to a linen bag 
and well squeezed under a screw-press. After being pulverised it 



1 P. 31, 283 and 631 ; A. 140, 284 ; B. 24, 2121. 



254 SPECIAL PART 

is heated to dusty dryness in an air-bath at no . Yield, about 
100 grammes. 

If even after long standing an abundant separation of crystals 
does not take place, the cause is probably due to the large per- 
centage of anhydride in the fuming sulphuric acid. Under these 
conditions it is diluted with concentrated acid, and the experiment 
repeated. If on the other hand the acid is too weak, the benzene 
will not dissolve in it. In this case, during the sulphonation the 
mixture is not cooled, and the reaction is allowed to take place at 

40-50°. 

In order to obtain pure sodium benzenesulphonate, 5 grammes 
of the crude product is crystallised from absolute alcohol, upon 
which it is noticed that the sodium chloride mixed with it is insol- 
uble in alcohol. 

(b) In order to obtain the by-product, sulphobenzide, 30 
grammes of the pulverised salt is warmed with 50 c.c. of ether, 
filtered with suction while hot, and washed with ether. After 
evaporating the ether, a small amount of a crystalline residue is 
obtained ; this is recrystallised in a test-tube from ligroi'n. Melt- 
ing-point, 1 2 9 . 

To prepare benzenesulphonchloride from sodium benzenesul- 
phonate, the extracted salt and unextracted salt are treated in a 
dry flask (under the hood) with finely powdered phosphorus pen- 
tachloride (for 3 parts dry sodium benzenesulphonate, use 4 parts 
phosphorus pentachloride). Mix by thorough shaking. The 
mixture is warmed £ to ^ hour on an actively boiling water-bath. 
The cold reaction-product is then poured gradually into ice-water 
in a flask (use ten times the weight of the sodium salt) ; it is shaken 
up from time to time, and, after standing for two to three hours, 
the sulphonchloride is taken up with ether and the generally turbid 
ethereal solution filtered ; the ether is then evaporated off. Yield, 
40-50 grammes. 

In a porcelain dish 10 grammes of finely powdered ammonium 
carbonate are treated with about 1 c.c. of benzenesulphonchloride, 
and rubbed together intimately ; the mixture is heated, with good 
stirring, over a small flame, until the odour of the sulphonchloride 



AROMATIC SERIES 255 

has vanished. After cooling, it is treated with water, filtered with 
suction, washed several times with water, and the benzenesulphon- 
amide crystallised from alcohol to which hot water is added until 
turbidity begins. Melting-point, 15 6°. 

Under the sulphonation of aniline it was mentioned that the aromatic 
compounds differ from the aliphatic compounds in that they can be 
sulphonated by the action of sulphuric acid ; i.e. the benzene-hydrogen 
atoms are replaced by the sulphonic acid group, S0 3 H. Thus the above 
reaction takes place in accordance with the following equation : 

/OH 
C 6 H 6 + S0 2 < - C 6 H 5 . SO3H + H 2 

\OH 

Since, in the sulphonation, an excess of sulphuric acid is always used, 
after the reaction is complete it is necessary to separate the sulphonic 
acid from the excess of sulphuric acid. Many sulphonic acids, espe- 
cially those of the hydrocarbons, are very easily soluble in water, so 
that the pure acid cannot be separated out on mere dilution with water, 
as is the case with sulphanilic acid. There are three methods in com- 
mon use for the isolation of sulphonic acids soluble in water. The 
sulphonic acids obtained most easily are those difficultly soluble in cold 
sulphuric acid. In this case it is only necessary to cool the sulphon- 
ating mixture, and filter off the sulphonic acid separating out, with 
suction over asbestos or glass-wool. A second method consists in 
allowing the sulphuric acid solution to flow into a saturated solution 
of common salt; in many cases the difficultly soluble (in sodium chlo- 
ride solution) sodium salt of the sulphonic acid separates out. Fre- 
quently it is more advantageous to use sodium acetate, potassium 
chloride, ammonium chloride, or other salts, instead of sodium chloride. 
Almost all soluble sulphonic acids, in the form of their alkali salts, can 
be separated by these two methods in the shortest time. In dealing 
with a new substance,- preliminary experiments with small quantities 
of the substance are made to determine which salt is best adapted for 
the separation. The third method, which is the one generally appli- 
cable, depends upon the property of sulphonic acids, of forming soluble 
salts of calcium, barium, and lead in contradistinction to sulphuric acid.. 
If the sulphuric acid solution, diluted with water, is neutralised with the 
carbonate of one of these metals and then filtered, the filtrate contains 
only the corresponding salt of the sulphonic acid, while the sulphuric 
acid in the form of calcium, barium, or lead sulphate remains on the 



256 SPECIAL PART 

filter. If the alkali salts of the sulphonic acids are- desired, the water 
solution of one of the above salts is treated with the alkali carbonate 
until a precipitate is no longer formed. The precipitate is filtered off, 
and the pure alkali salt of the sulphonic acid is obtained in solution, 
which, on evaporation to dryness, yields the salt in the solid condition. 

In order to obtain the free sulphonic acid, the lead salt is prepared 
and then decomposed with sulphuretted hydrogen. 

The sulphonic acids of the hydrocarbons are generally colourless, 
crystallisable compounds, very easily soluble in water, behaving like 
strong acids. By heating with hydrochloric acid, under pressure if 
necessary, or by the action of steam, the sulphonic acid group may be 
split off, e.g. : 

C 6 H 5 . SO3H + H 2 = C 6 H 6 + H 2 S0 4 

This reaction is of importance in many cases for the separation of 
hydrocarbon mixtures. If under certain conditions one hydrocarbon 
is sulphonated, and another is not, the latter can be separated from the 
former by removing the sulphuric acid solution of the sulphonic acid 
of the first, and from this the original hydrocarbon may be regenerated 
by one of the methods mentioned. 

Of particular importance is the behaviour of sulphonic acids when 
fused with caustic potash or caustic soda, by which the sulphonic acid 
group is eliminated and a phenol formed : 

C 6 H 5 . S0 3 K + KOH = C 6 H 5 . OH + K 2 S0 3 

With benzenesulphonic acid this important reaction does not take 
place smoothly ; for this reason the directions for carrying it out prac- 
tically will be given later in another place (see /3-naphthol). Poly- 
acid phenols may also be obtained from poly-basic sulphonic acids. 
The formation of m-dioxybenzene or resorcinol from benzenedisul- 
phonic acid is of practical value : 



C 6 H 4 (S0 3 K) 2 + 2 KOH = C 6 H 4 < 



,OH 



^OH 



If an alkali salt of a sulphonic acid mixed with potassium cyanide or 
potassium ferrocyanide is subjected to dry distillation, the sulphonic 
acid group is replaced by cyanogen and an acid-nitrile is obtained, e.g. : 

C 6 H 5 . SO3K + KCN = C 6 H 5 . CN + K 2 S0 3 

Benzonitrile 



AROMATIC SERIES 257 

The sulphonic acids behave toward phosphorus pentachloride like the 
carbonic acids, with the formation of acid-chlorides : 

C 6 H 5 . S0 3 Na + PC1 5 = C 6 H 5 . S0 2 . CI + NaCl + POCl 3 

The sulphonchlorides differ from the carbonic acid chlorides, in that 
they are not decomposed by cold water. In order to separate them 
from the phosphorus oxychloride, the mixture is generally poured into 
cold water ; after long standing the oxychloride is converted into phos- 
phoric acid, and the acid-chloride insoluble in water is obtained by 
decanting the water or extracting with ether ; or in case it is solid, by 
filtering. The sulphonchlorides are generally distinguished by a very 
characteristic odour. They can be distilled in a vacuum only, without 
decomposition. Treated with ammonia they form sulphonamides, which 
crystallise well and are used for the characterisation of the sulphonic 
acids : 

C 6 H 5 . S0 2 . CI + NH 3 = C 6 H- . S0 2 . NH 2 + HC1 

In the sulphonamides, in consequence of the strongly negative 
character of the X . S0 2 -group, the hydrogen of the amido-group is 
so easily replaced by metals, that they dissolve in water solutions of 
the alkalies to form salts of the amide. (Try it.) If a sulphon- 
chloride is allowed to stand a long time with an aliphatic alcohol, a 
sulphonic acid ester is formed, e.g. : 

C 6 H 5 . S0 2 . CI + C 2 H 5 . OH = C 6 H 5 . S0 2 . OC 2 H 5 + HC1 

Benzenesulphonic ester 

If this is now warmed with an alcohol, an aliphatic ether is formed, 
with the generation of the sulphonic acid, e.g. : 

C 6 H 5 . S0 2 . OC 2 H 5 + C 2 H 5 . OH = C 6 H 5 . S0 3 H + C 2 H 5 . . C 2 H 5 

The formation of ether in this case is analogous to the formation of 
ethyl ether on heating ethyl sulphuric acid with alcohol : 

/)C 2 H 5 
S0 2 + C 2 H 5 . OH = H 2 S0 4 + C 2 H 5 . . C 2 H 5 

\dh 

Since this reaction is continuous, and since the benzene sulphonic acid 
formed in the reaction is a weaker acid than sulphuric acid, and conse- 



258 SPECIAL PART 

quently does not carbonise the alcohol like sulphuric acid, the operation 
may be continued for a long time uninterruptedly. For these reasons 
recently attempts have been made to employ the aromatic sulphonic 
acids for the technical preparation of ether. If the sulphonation is 
effected as above with fuming sulphuric acid, in many cases, besides 
the sulphonic acid a small quantity of sulphone is formed, e.g. : 



2 C 6 H 6 + S0 3 = S0 2 + H 2 
X C 6 H 3 

Diphenylsulphone 
= Sulphobenzide 

For sulphonating purposes, either ordinary concentrated sulphuric acid 
or the so-called monohydrate or fuming sulphuric acid of various grades 
is used, according to the conditions. The reaction is conducted with 
cooling, at the room temperature, or with heating. 

To facilitate the elimination of water, phosphorus pentoxide or 
potassium sulphate' may be added to the sulphonating mixture. 

In some cases it is of advantage to use chlorsulphuric acid instead 
of sulphuric acid ; the reaction takes place in accordance with the fol- 
lowing equation : 

C,H 6 + CI . SOoH = C,H, . SO,H + HC1 



20. REACTION: REDUCTION OF A SULPHONCHLORIDE TO A 
SULPHINIC ACID OR TO A THIOPHENOL 

Examples: (a) Benzenesulphinic Acid. 1 (b) Thiophenol 2 

(a) Heat 40 grammes of water to boiling in a 300 c.c. flask 
provided with a short reflux condenser and a dropping funnel ; 
add 10 grammes of zinc dust, and without further heating by the 
flame, gradually allow to flow in from the funnel, with thorough 



1 B. 9, 1585. 2 A. 119, 142. 



AROMATIC SERIES 259 

shaking, 15 grammes of benzenesulphonchloride in small portions. 
After each addition wait until the vigorous reaction accompanied 
by a hissing sound has moderated. The mixture is then heated 
a few minutes over a small flame, filtered after cooling from the 
precipitate of zinc dust and the zinc salt of benzenesulphinic acid, 
and the precipitate washed several times with water. The insig- 
nificant-looking gray precipitate is the reaction-product, and not 
the filtrate, which can be thrown away. The precipitate is then 
heated for about ten minutes, not quite to boiling, with a solution 
of 10 grammes of dehydrated sodium carbonate in 50 c.c. of water, 
and then filtered with suction. The precipitate remaining on the 
filter is worthless, while the filtrate contains the sodium benzene- 
sulphinate in solution. This is evaporated to about one-half its 
original volume, and, after cooling, acidified with dilute sulphuric 
acid, upon which the free benzenesulphinic acid separates out in 
colourless crystals ; the separation is facilitated by rubbing the 
sides of the vessel with a glass rod. After filtering, the substance 
is recrystallised from a little water. Melting-point, 83-84 . 

Should the free acid not separate on acidifying the sodium salt, 
it is extracted several times with ether; this is evaporated, and 
the residue, in case it does not solidify of itself, is rubbed with a 
glass rod and then recrystallised. 

(6) In order to convert the residue of benzenesulphonchloricLe 
obtained in Reaction 19 into thiophenol, it is heated on a water- 
bath with granulated tin and concentrated hydrochloric acid, in a 
large flask provided with a long reflux condenser and dropping 
funnel ; the sulphonchloride is allowed to flow in gradually from 
the dropping funnel. (To 1 part of the chloride use 2\ parts of 
tin and 5 parts of concentrated acid.) The heating is continued 
until most of the tin is dissolved. The thiophenol formed is dis- 
tilled over with steam, extracted with ether, dried over anhydrous 
Glauber's salt, and, after the evaporation of the ether, rectified. 
Boiling-point, 173 . 

In the preparation of thiophenol, care is taken that there are 
no flames in the neighbourhood of the flask in which the reaction 
is conducted, otherwise there may be an explosion of the mixture 



26o SPECIAL PART 

of oxygen and hydrogen. Since the thiophenol possesses an 
extremely unpleasant odour, and the vapours attack the eyes, 
causing tears, the experiment must not be carried out in the 
laboratory, but in a side room (hydrogen sulphide room), or in 
the open air, in the basement, or at least under a hood with a 
good draught. Further, care must be taken not to allow the 
substance to come in contact with the skin, since it produces a 
violent burning. 

If zinc dust is allowed to act on a sulphonchloride, the zinc salt of 
the sulphinic acid is formed : 

C 6 H 5 .S0 2 .C1 C 6 H 5 .S0 2 \ 

yZn + ZnCl 2 
C 6 H 5 . S0 2 . CI + ZnZn - C 6 H 5 . SO/ 

Zinc benzenesulphinate 

The zinc salts thus formed are insoluble in water, and can be easily 
obtained by filtering off. In order to prepare the free sulphinic acid 
from a zinc salt, it is first converted into the easily soluble sodium salt 
by boiling with a sodium carbonate solution ; the solution of the sodium 
salt is concentrated, and the free acid is precipitated with dilute sulphuric 
acid. The sulphinic acids differ from the sulphonic acids in that they 
are difficultly soluble in cold water, and can, therefore, be recrystallised 
from water. On fusing with potassium hydroxide, the sulphinic acids 
pass over to the hydrocarbons : 

C 6 H 5 . S0 2 K + KOH = K 2 S0 3 + C 6 H 6 

If they are reduced, a thiophenol is finally obtained, as above : 

C 6 H 5 . S0 2 H + 4 H = C 6 H 5 . SH + 2 H 2 

The thiophenols may also be prepared by the direct reduction of the 
sulphonchlorides : 

C 6 H 5 . S0 2 C1 + 6 H = C 6 H 5 . SH + 2 H 2 + HC1 

The thiophenols are liquids of unpleasant odours ; the higher mem- 
bers of the series are solids. Like the mercaptans of the aliphatic 
series, they form difficultly soluble salts with lead and mercury. 



AROMATIC SERIES 26l 

Experiment : Dissolve mercuric chloride or lead acetate in a 
test-tube with alcohol by heating ; then cool, and filter. If the 
alcoholic solution is treated with a few drops of thiophenol, a 
precipitate of the difficultly soluble salt is obtained. The lead 
salt is yellow, and possesses the composition represented by the 
formula : 

(C 6 H 5 .S) 2 Pb 

In the air, and on treatment with oxidising agents like nitric acid, 
chromic acid, etc., the thiophenols are oxidised to disulphides : 

2 C 6 H 5 . SH + O = C 6 H 5 . S— S . C 6 H 5 + H 2 

Experiment : A few drops of phenyl mercaptan are dissolved in 
alcohol, treated with some ammonia, and evaporated to dryness on 
the water-bath in a watch-glass. (Under the hood.) Colourless 
needles of the disulphide remain. Melting-point, 6i°. 

By reduction the disulphides are easily converted back to the thio- 
phenols : 

C 6 H 5 . S— S . C 6 H 5 + 2 H = 2 C 6 H 5 . SH 

Like the phenols the thiophenols have the power of forming ethers, 
e.g. : 

C 6 H 5 . SCH 3 = Thioanisol, 
C 6 H 5 . S . C 6 H 5 = Phenylsulphide. 



21. REACTION : SULPHONATION OF AN AROMATIC HYDRO- 
CARBON (II) 

Example : p-Naphthalenesulphonic Acid 

A mixture of 50 grammes of finely pulverised naphthalene and 
60 grammes of pure concentrated sulphuric acid is heated in an 
open flask in an oil-bath for 4 hours to 170-180 . After cool- 
ing, the solution is carefully poured, with stirring, into 1 litre of 
water, and the naphthalene not attacked is filtered off; in case 
the filtration takes place very slowly, only the turbid liquid is 
poured off from the coarse pieces of naphthalene ; the mixture is 



262 SPECIAL PART 

neutralised at the boiling temperature in a large dish with a paste 
of lime, not too thin, prepared by triturating about 70 grammes 
of dry slaked lime with water. The mixture is filtered while hot 
as possible through a filter-cloth, which has been previously 
thoroughly moistened (see page 56) and the precipitate washed 
with hot water. The filter-cloth is then folded together and 
thoroughly squeezed out in another dish ; the expressed, generally, 
turbid liquid, after filtering, is united with the main quantity. 
The solution is then evaporated in a dish over a free flame until 
a test-portion will solidify to a crystalline paste on rubbing with a 
glass rod. After the solution has been allowed to stand over night 
the calcium /?-naphthalenesulphonate is filtered off with suction, 
washed once with a little water, pressed firmly together with a 
pestle, and spread out on a porous plate. In order to obtain the 
sodium salt, it is dissolved in hot water, and the solution gradually 
treated with a concentrated solution of 50 grammes of crystallised 
sodium carbonate until a test-portion filtered off no longer gives 
a precipitate with sodium carbonate. After cooling, the precipi- 
tate of calcium carbonate is filtered off with suction, washed with 
water, and the filtrate evaporated over a free flame until crystals 
begin to separate from the hot solution. After standing several 
hours at the ordinary temperature, the crystals are filtered off, and 
the mother-liquor further concentrated ; after long standing, the 
second crystallisation is filtered off, and the mixture of the two 
lots of crystals dried on the water-bath. Yield, 60-70 grammes. 

Naphthalene is sulphonated on heating with sulphuric acid, in ac- 
cordance with the following equation : 

C 10 H 8 + H 2 S0 4 = C 10 H 7 . SO3H + H 2 0. 

There is formed not as in the case of benzene, in which the six 
hydrogen atoms are equivalent, a single sulphonic acid, but a mixture 
of two isomeric sulphonic acids : 



SO3H 





and i S °3 H - 



o-Naphthalenesulphonic acid |3-Naphthalenesulphonic acid 



AROMATIC SERIES 263 

According to the temperature at which the sulphonation takes place, 
more of one than of the other acid is formed ; at lower temperatures an 
excess of the a-acid is obtained, at higher an excess of the /3-acid. If 
the mixture is heated to ioo°, a mixture of 4 parts of the a-acid and 
1 part of the /3-acid is formed, while at 170 a mixture of the 3 parts of 
the /3-acid and 1 part of the a-acid is obtained. In order to separate 
the sulphonic acids from the excess of sulphuric acid, advantage is 
taken of the fact that sulphonic acids differ from sulphuric acid in that 
they form soluble salts of calcium, barium, and lead, as mentioned 
under benzenesulphonic acid. For the separation of the sulphonic acid 
from sulphuric acid, the calcium salt is prepared by neutralising the 
acid mixture with chalk or lime, since it is cheaper than lead carbonate 
or barium carbonate. This method is followed technically on the large 
scale as well as in laboratory preparations. Since the calcium salts of 
the two isomeric sulphonic acids possess a very different solubility in 
water, — at io° 1 part of the a-salt dissolves in 16.5 parts of water, and 
1 part of the (3-s3.lt dissolves in 76 parts of water, — the /3-salt, which is 
more difficultly soluble, and consequently crystallises out first, can be 
separated by fractional crystallisation from the a-salt which remains in 
solution. For the conversion into naphthol the calcium salt cannot be 
used directly ; it must first be changed into the sodium salt by treatment 
with sodium carbonate : 

(C 10 H 7 . S0 3 ) 2 Ca + Na 2 C0 3 = 2 C 10 H» . S0 3 Na + CaC0 3 . 

In order to remove the last portions of the a-salt, it is advisable not 
to evaporate the solution of sodium salt directly to dryness, but to 
allow the more difficultly soluble /3-salt to crystallise out, upon which 
the a-salt remains dissolved in the mother-liquor. 

The reactions of the naphthalenesulphonic acids are similar to those 
given above under benzenesulphonic acid. It is still to be mentioned 
that the a-acid is converted into the /3-acid by heating with concen- 
trated sulphuric acid to almost 200 ; a reaction which is explained by 
the fact that the sulphonic acid decomposes in the small amount of water 
always present, into naphthalene and sulphuric acid, and that the 
former is then sulphonated to the /?-acid at the higher temperature 
(200 ) . The sulphonation of naphthalene to the a- and /3-acids is 
carried out on the large scale in technical operations, since when fused 
with sodium hydroxide these acids yield naphthols of great importance 
for the manufacture of dyes. The next preparation deals with this 
reaction. 



264 SPECIAL PART 



22. REACTION: CONVERSION OF A SULPHONIC ACID INTO A 

PHENOL 

Example : p-Naphthol from Sodium-p-Naphthalene Sulphonate and 
Sodium Hydroxide 1 

In order to convert sodium-/?-naphthalene sulphonate into 
/?-naphthol the proportions of the necessary reagents used are : 

10 parts sodium-/3-naphthalene sulphonate; 
30 parts sodium hydroxide, as pure as possible ; 
1 part water. 

The sodium hydroxide is broken in pieces about a centimetre in 
length, or the size of a bean, treated with the water, and heated 
in a nickel crucible (a crucible 11 cm. high and 8 cm. in diameter 
is a convenient size), with stirring, to 280 (Fig. 73). The stirring 
is done with a thermometer, the lower end of which is protected 
by a case of copper or nickel, about 16 cm. long and 8 mm. wide. 
This is supported by a cork, containing a narrow canal at the 
side, fitting the case. In order to be able to determine the tem- 
perature as exactly as possible, a layer of oil 1 cm. high is placed 
in the case, in which the bulb of the thermometer is immersed. 
If the stirring is done with the case, the upper portion is covered 
with several layers of asbestos board, secured with wire, or a cork 
is pushed over the case (Fig. 73). Since, on fusion of the sodium 
hydroxide, a troublesome spattering takes place, the hand is 
protected by a glove, and the eyes by glasses. As soon as the 
temperature reaches 280 , the heating is continued with a some- 
what smaller flame, and the sodium naphthalene sulphonate is 
gradually added, with stirring. After each new addition, the tem- 
perature falls somewhat ; no more of the salt is added, until the 
temperature again reaches 280 . After all the salt is added, the 
flame is made somewhat larger, upon which the fusion becomes 
viscid with evolution of steam and frothing, until finally, at about 
310 , the real reaction takes place. After the temperature is held 



1 E. Fischer-Kling, Prep, of Organic Compounds, page 54. Z. 1867, 299. 



AROMATIC SERIES 



265 



at 310-320 for about 5 minutes, the fusion becomes liquid, and 
the reaction is complete. The melted mass is then poured on a 
strong copper plate the edges of which have been turned up and of 
sufficient size so that the bottom is covered 
by a thin layer of the mass. The portions 
of dark sodium naphtholate may be easily 
distinguished from the brighter caustic 
soda. After cooling, the solid mass is 
broken up and dissolved in water. The 
naphthol is precipitated at the boiling 
temperature with concentrated hydro- 
chloric acid (under the hood), and after 
cooling is extracted with ether. The 
ethereal solution is dried over anhydrous 
Glauber's salt, and then the ether is 
evaporated in an apparatus similar to 
the one described on page 35 ; a frac- 
tionating flask with a very wide condens- 
ing tube is used. After the removal of 
the ether, the naphthol remaining back is 
distilled over without the use of a condenser. Melting-point, 
123 . Boiling-point, 286 . Yield, half the weight of the sul- 
phonate used. 




FIG. 73. 



As above indicated, in a sodium hydroxide, or potassium hydroxide 
fusion of a sulphonic acid, besides the phenol, the alkali sulphite is 
formed, e.g. : 

C 10 H- . S0 3 Na + 2 NaOH = C 10 H 7 . ONa + Na 2 S0 3 + H,0 

Sodium naphtholate 



The free phenol is, therefore, not directly obtained on fusion, but 
the alkali salt of it, from which, after the solution of the fusion in water, 
the phenol is liberated on acidifying with hydrochloric acid. 

The reaction just effected is in practice carried out on the largest 
scale in iron kettles to which stirring apparatus is attached. /3-naph- 
thol as well as its numerous mono- and poly-sulphonic acid derivatives 
obtained by treatment with sulphuric acid find extensive application for 



266 SPECIAL PART 

the manufacture of azo dyes. Further, from the /3-naphthol, /3-naph* 
thylamine is prepared by the action of ammonia under pressure : 

C 10 H 7 .OH + NH 3 = C 10 H 7 .NH 2 + H 2 0, 

which also finds technical use for the manufacture of azo dyes, as such 
and in the form of its sulphonic acids. a-Naphthol is also prepared in 
the same way by fusion of a-sodiumnaphthalene sulphonate with sodium 
hydroxide, although not in so large quantities as the /8-naphthol. 

The phenols, in consequence of the negative character of the aromatic 
hydrocarbon residue, are weak acids which dissolve in water solutions 
of the alkalies to form salts. Still the acid nature is so weak that the 
salts can be decomposed by carbon dioxide ; use is frequently made of 
this property for the purification and separation of phenols. 

Experiment : A mixture of /3-naphthol and benzoic acid is 
dissolved in a diluted caustic soda solution, and carbon dioxide 
passed into it for a long time. /3-Naphthol only separates out; 
this is filtered off. The filtrate is acidified with concentrated 
hydrochloric acid upon which the benzoic acid is precipitated. 

The naphthols differ from the phenols of the benzene series, in that 
their hydroxyl groups are more capable of reaction than those of the 
phenols, cresols, etc. While, for example, the ether of phenol cannot 
be prepared from the phenol and corresponding alcohol by abstracting 
water : 

(C G H 5 .OH + CH3.OH = C 6 H 5 .O.CH 3 + H 2 0), 

Does not take place 

but can only be obtained by the action of halogen alkyls on phenol 
salts : 

C 6 H 5 .ONa + ICH3 = C 6 H 5 .O.CH 3 + Nal. 

By heating the naphthols with an aliphatic alcohol and sulphuric acid, 
the ethers are easily prepared : 

C 10 H 7 .OH + CH3.OH = C 10 H 7 .O.CH 3 + H 2 0. 

Naphthylmethyl ether 



AROMATIC SERIES 267 

23. REACTION: NITRATION OF A PHENOL 
Example : 0- and p-Nitrophenol 

Dissolve 80 grammes of sodium nitrate in 200 grammes of 
water by heating; after cooling, the solution is treated, with 
stirring, with 100 grammes of concentrated sulphuric acid. To 
the mixture cooled to 25 contained in a beaker, add drop by 
drop, from a separating funnel, with frequent stirring, a mixture 
of 50 grammes of crystallised phenol and 5 grammes of alcohol, 
melted by warming. During this addition the temperature is kept 
between 25-30 by immersing the beaker in water. Should the 
phenol solidify in the separating funnel, it is again melted by a 
short warming in a large flame. After the reaction-mixture has 
been allowed to stand for two hours, with frequent stirring it is 
treated with double its volume of water ; the reaction-product 
collects as a dark oil at the bottom of the vessel. The principal 
portion of the water solution is then decanted from the oil, this is 
washed again with water, and after the addition of ^ litre of water, 
is distilled with steam until no more o-nitrophenol passes over. 
Concerning the removal of the o-nitrophenol solidifying in the 
condenser, see page 37 (temporary removal of the condenser- 
water). 

After cooling, the distillate is filtered, the o-nitrophenol washed 
with water, pressed out on a porous plate, and dried in a desic- 
cator. Since it is obtained completely pure, it is unnecessary to 
subject it to any further process of purification. In order to 
obtain the non-volatile p-nitrophenol remaining in the flask, the 
mixture is cooled by immersion in cold water, the water solution 
is filtered from the undissolved portions, and the filtrate boiled for 
a quarter-hour with 20 grammes of animal charcoal, the water 
evaporating being replaced by a fresh quantity. The charcoal is 
then filtered off and the filtrate allowed to stand in a cool place 
over night, upon which the p-nitrophenol separates out in long, 
almost colourless needles. The oil still present in the distillation 
flask is boiled with a mixture of 1 part by volume of concentrated 



268 SPECIAL PART 

hydrochloric acid and 2 parts by volume of water, with the addi- 
tion of animal charcoal, filtered after partial cooling and the fil- 
trate allowed to stand over night. There is thus obtained a 
second crystallisation. If the crystals which have separated out 
are still contaminated by the oil, they are recrystallised from 
dilute hydrochloric acid with the use of animal charcoal. 

Melting-point of o-Nitrophenol, 45 ° ; 
Melting-point of p-Nitrophenol, 114 . 

Yield, 30 grammes and 5-10 grammes respectively. 

The mon-acid phenols of the benzene series are, in contrast to the 
corresponding hydrocarbons, very easily nitrated. In the nitration of 
benzene, in order to facilitate the elimination of the water, concen- 
trated sulphuric acid must be added ; whereas the action of concen- 
trated nitric acid alone upon phenol is so energetic, that in this case 
it must be diluted with water. Upon nitrating phenol, the o- and 
p-nitrophenols are formed simultaneously, the former of which is vola- 
tile with steam : 

/N0 2 
C 6 H 5 . OH + NO,. OH = C 6 H 4 < + H 2 0. 

X)H 

o- and p-Nitrophenol 

On nitrating the homologues of phenol, the nitro-groups always enter 
the o- and p-positions to the hydroxyl group, and never the m-position. 
In order to prepare m-nitrophenol, it is necessary to start from m-nitro- 
aniline ; this is diazotised and its diazo-solution boiled with water. 

The nitrophenols behave in all respects like the phenols. But by 
the entrance of the negative nitro-group, the negative character of the 
phenol is so strengthened that the nitrophenols not only dissolve in 
alkalies, but also in the alkali carbonates. 

Experiment : Dissolve some o-nitrophenol in a solution of 
sodium carbonate by warming ; the scarlet red sodium salt is 
formed. 

In consequence of this action, the nitrophenols cannot be precipi- 
tated from their alkaline solutions by carbon dioxide. 

In addition the nitrophenols show the characteristics of the nitro- 
compounds in general, since they, for example, pass over to amido- 
phenols on energetic reduction, etc. 



AROMATIC SERIES 



269 



24. REACTION: (a) CHLORINATION OF A SIDE-CHAIN OF A HYDRO- 
CARBON, {b) CONVERSION OF A DICHLORIDE INTO AN ALDEHYDE 

Examples : (a) Benzalchloride from Toluene 

(b) Benzaldehyde from Benzalchloride 

(a) A 100 c.c. round flask with a wide neck (Fig. 74) con- 
taining 50 grammes of toluene is placed in a well-lighted posi- 
tion, best in the sunlight. The toluene is heated to boiling 
and a current of dry chlorine conducted into it until its weight 




Fig. 74. 

is increased by 40 grammes. In order to be able to judge 
of the course of the reaction, the flask, with the toluene, is 
weighed before the experiment. By interrupting the passage of 
the chlorine from time to time, cooling and weighing the flask, 
the increase in weight will indicate how far the chlorinating action 



270 SPECIAL PART 

has proceeded. The length of the operation varies greatly. In 
summer the reaction is complete in a few hours ; during the 
cloudy days of winter a half or a whole day may be necessary. 
The reaction may be materially assisted by adding 4 grammes of 
phosphorus pentachloride to the toluene. 

(b) In order to convert the benzalchloride into benzaldehyde, 
the crude product thus obtained is treated in a round flask pro- 
vided with an effective reflux condenser, with 500 c.c. of water 
and 150 grammes of precipitated calcium carbonate (or floated 
chalk or finely pulverised marble) and the mixture heated four 
hours in a hemispherical oil-bath to 130 (thermometer in the 
oil). Without further heating, steam is passed through the hot 
contents of the flask until no more oil distils over. For this pur- 
pose the apparatus necessary (cork with a glass tube) has been 
prepared before the heating in the oil-bath. 

Before the crude benzaldehyde is subjected to purification, the 
liquid remaining in the distilling flask is filtered while hot through 
a folded filter, and the filtrate acidified with much concentrated 
hydrochloric acid. On cooling, the benzoic acid obtained as a 
by-product in the preparation of benzaldehyde separates out in 
lustrous leaves. It is filtered off and recrystallised from hot water, 
during which it must not be heated too long, since it is volatile 
with steam. Melting-point, 121 . 

The oil passing over with the steam is treated, together with all 
of the liquid, with a concentrated solution of sodium hydrogen 
sulphite, until after long shaking the greater part of the oil has 
passed into solution. Should crystals of the double compound of 
benzaldehyde and sodium hydrogen sulphite separate out, water is 
added until they are dissolved. The water solution is then filtered 
through a folded filter from the oil remaining undissolved, and 
the filtrate treated with anhydrous sodium carbonate until it shows 
a strong alkaline reaction. This alkaline liquid is now subjected 
to distillation with steam, when perfectly pure benzaldehyde passes 
over • it is taken up with ether, and, after the evaporation of the 
ether, is distilled. Boiling-point, 179 . 

Under the preparation of brombenzene it has already been men- 
tioned that by the action of chlorine or bromine on aromatic hydro- 
carbons containing aliphatic side-chains, different products are formed, 



AROMATIC SERIES 27 1 

depending on the temperature at which the action takes place. If, e.g., 
chlorine acts at lower temperatures on toluene, chlortoluene is formed, 
the chlorine entering the benzene ring : 

/CH 3 

C G H 5 . CH 3 + Cl 2 = C 6 H 4 < + HC1. 

At ordinary temperatures Chlortoluene 

If, on the other hand, chlorine is conducted into boiling toluene, the 
chlorine atom enters the side-chain : 

C G H-.CH 3 + Cl 2 = C 6 H 5 .CH 2 C1 + HC1. 

At boiling temperature Benzylchloride 

If chlorine is conducted into toluene at the boiling temperature for 
a long time, a second, and finally a third, hydrogen atom of the methyl 
group is substituted : 

C C H 5 .CH 2 C1 + Cl 2 = C 6 H 5 .CHC1 2 + HC1 

Boiling Benzalchloride 

C 6 H 5 . CHC1 2 + Cl 2 = C 6 H S . CClo + HC1. 

Benzotrichloride 

The formation of benzotrichloride is the final result of the action 
of chlorine under these conditions, since the benzotrichloride is not 
changed even by passing in the chlorine for a longer time. 

The replacement of hydrogen by chlorine directly presents the diffi- 
culty, unlike the liquid bromine, that weighed quantities cannot be 
used, and the exact point to which the introduction of chlorine should 
be continued in order to get a certain definite compound must be 
determined. This is accomplished if, from time to time, the increase 
in weight of the substance being chlorinated is determined. Since 
the conversion of one molecule of toluene to benzylchloride requires 
an increase of weight equal to the atomic weight of chlorine minus the 
atomic weight of hydrogen (CI — H = 34.5), therefore in the prepara- 
tion of benzylchloride, 100 parts by weight of toluene must take up 
an additional weight of chlorine = 37-5 parts by weight, and corre- 
spondingly in the preparation of benzalchloride or benzotrichloride, 
the increase in parts by weight must be respectively 2 x 37.5 = 75 
and 3 x 37.5 = 112. 5. 

In most organic chlorinating reactions, besides the main reaction, a 
side reaction also takes place which, in the above example, results in 
the conversion of a portion of the toluene to benzalchloride and 



272 SPECIAL PART 

benzotrichloride, while another portion is only chlorinated to benzyl 
chloride. Accordingly the reaction-product obtained above consists 
essentially of benzalchloride mixed with a small quantity of benzyl 
chloride and benzotrichloride. 

The halogen derivatives of the aromatic hydrocarbons containing 
the halogen in the side-chain are in part liquids, in part colourless crys- 
tallisable solids, which are distinguished from their isomers containing 
the halogen in the benzene ring, in that their vapours violently attack 
the mucous membrane of the eyes and nose. Care is taken therefore 
in the above preparation not to expose the face to the vapours, and 
further to prevent the chlorination products from coming in contact 
with the hands. 

Concerning their chemical properties, these two isomeric series differ 
in that the compounds containing the halogen in the side-chain are far 
more active than those in which the halogen occurs in the benzene 
ring, as is apparent from the following equations : 

C 6 H 5 . CH 2 C1 + NH 3 = C 6 H 5 . CH 2 . NH 2 + HC1 

Benzylamine 

C 6 H 5 . CH 2 C1 + CH 3 . COONa = CH 3 . CO . OCH 2 . C 6 H 5 + NaCl 

Benzylacetate 

C 6 H 5 . CH 2 C1 + KCN = C 6 H 5 . CH 2 . CN + KC1 

Benzyl cyanide 

The chlorides obtained by substituting a side-chain are of importance 
for making certain preparations, — the aromatic alcohols, aldehydes, 
and acids. On boiling with water, they decompose, in accordance with 
the following equations : 

(i) C 6 H 5 . CH 2 C1 + H 2 = C 6 H 5 .CH 2 .OH + HC1 

Benzyl alcohol 

(2) C 6 H 5 . CHC1 2 + H 2 = C 6 H 5 . CHO + 2 HC1 

Benzaldehyde 

(3) C ( .H 5 . CC1 3 + 2 H 2 = C 6 H 5 . CO . OH + 3 HC1 

Benzoic acid 

If the halogen atom is in the ring, none of these transformations will take 
place. But since, in cases 1 and 2, the hydrochloric acid formed in the re- 
action acts in the opposite way and may regenerate the original chloride, it 
must be neutralised. This is usually accomplished by the addition of a 
carbonate, upon which the acid acts with the liberation of carbon dioxide. 



AROMATIC SERIES 273 

In practice, the cheap calcium carbonate (marble dust) is used, and the 
above method for the preparation of benzaldehyde is, as far as possible, 
an imitation of the technical process used for obtaining the substance. 
From benzylchloride, benzaldehyde may also be prepared directly by 
boiling it with water in the presence of lead nitrate or copper nitrate. 
From the benzylchloride, benzyl alcohol is first formed, which is oxi- 
dised by the nitrate to benzaldehyde. 

As above mentioned, the chlorination product obtained consists 
essentially of benzalchloride, mixed with small amounts of benzyl- 
chloride and benzotrichloride. If the mixture is boiled with water, 
with the addition of calcium carbonate, a mixture consisting mainly of 
benzaldehyde, besides benzylchloride and benzoic acid — the latter 
being converted into the calcium salt by the carbonate — is obtained. 
If the reaction-mixture is distilled with steam, benzaldehyde, benzyl 
alcohol, and a small amount of chlorides which have not taken part 
in the reaction, pass over with the steam, while the calcium benzoate 
remains in the distillation flask. By acidifying the residue, the free 
benzoic acid may be obtained as above. A large proportion of the 
so-called " benzoic acid from toluene " is obtained in this way as a 
by-product in the technical preparation of benzaldehyde. In order to 
separate the benzaldehyde from benzyl alcohol, the chlorides, and other 
impurities, advantage is taken of the general property of aldehydes of 
uniting with acid sodium sulphite to form soluble double compounds. 
If the distillate is shaken with a solution of sodium hydrogen sulphite, 
the aldehyde dissolves, while the impurities remain undissolved. These 
are filtered off, and the sulphite compound of the aldehyde decomposed 
with sodium carbonate ; on a second distillation with steam, the pure 
aldehyde passes over. 

The aromatic aldehydes are in part liquids, in part solids, possessing 
a pleasant aromatic odour. 

They show the characteristic aldehyde reactions, yielding primary 
alcohols on reduction and carbonic acids on oxidation. 

Experiment : A few drops of benzaldehyde are allowed to 
stand in a watch-glass in the air. After a long time, crystals of 
benzoic acid appear. 

C 6 H 5 .CHO + O = C G H 5 .CO.OH. 

That they unite with acid sulphites to form crystalline compounds has 
been mentioned : 



274 SPECIAL PART 

/OH 
C 6 H 5 . CHO + HS0 3 Na = C 6 H 5 . CH 

\S0 3 Na 

Experiment : To \ c.c. of benzaldehyde add a concentrated 
solution of sodium hydrogen sulphite, and shake. The mixture 
solidifies after a short time to a crystalline mass. 

Further, the aldehydes react, as mentioned under acetaldehyde, with 
hydroxylamine and phenyl hydrazine, to form oximes and hydrazones. 
With hydrazine they yield, according to the experiment conditions, the 
not very stable hydrazines or the more stable and characteristic azines : 

C 6 H 5 . CH 10+H 2 1 N - NH 2 = H 2 + C 6 H 5 . CH=N . NH 2 

Benzalhydrazine 

C 6 H 5 . CH [Q + H 2 | N C 6 H 5 . CHzzN 

|=2H 2 + I 

C 6 H 5 . CH lQ + H 2 [ N C 6 H 5 . CHzzN 

Benzalazine 

Aldehydes also condense readily with primary aromatic bases with the 
elimination of water : 

C 6 H 5 . CHO + C 6 H 5 . NH 2 = C 6 H 5 . CHzzN . C 6 H 5 + H 2 

Benzylideneaniline 

Experiment : In a test-tube make a mixture of 1 c.c. of benzal- 
dehyde and 1 c.c. of pure aniline, and warm gently. On cooling, 
drops of water separate out, and the mixture solidifies, crystals of 
benzylideneaniline being formed. 

An additional number of characteristic aldehyde reactions will be 
taken up later in practice. Benzaldehyde is prepared technically on 
the large scale. Its most important application is for the manufacture 
of the dyes of the Malachite Green series, and of cinnamic acid (see 
these preparations). 

25. REACTION: SIMULTANEOUS OXIDATION AND REDUCTION OP 
AN ALDEHYDE UNDER THE INFLUENCE OF CONCENTRATED 
POTASSIUM HYDROXIDE 

Example : Benzoic Acid and Benzyl Alcohol from Benzaldehyde x 

Treat 20 grammes of benzaldehyde in a stoppered cylinder or a 
thick- walled vessel with a cold solution of 18 grammes of potas- 
sium hydroxide in 1 2 grammes of water, and shake until a perma- 
nent emulsion is formed ; the mixture is then allowed to stand 
over night. The vessel is closed by a cork, and not a glass 
stopper, since at times a glass stopper becomes so firmly fastened 
that it can be removed only with great difficulty. To the crys- 

1 B. 14, 2394. 



AROMATIC SERIES 275 

talline paste (potassium benzoate) separating out, water is added 
until a clear solution is obtained from which the benzyl alcohol is 
extracted by repeatedly shaking with ether. After the evapora- 
tion of the ether the residue is subjected to distillation ; benzyl 
alcohol passes over at 206 . Yield, about 8 grammes. The ben- 
zoic acid is precipitated from the alkaline solution on acidifying 
with hydrochloric acid. 

While many aliphatic aldehydes (see acetaldehyde) are converted 
by alkalies into more complex compounds, with higher molecular 
weights, the so-called aldehyde resins, the aromatic aldehydes under 
similar conditions react smoothly ; two molecules are decomposed by 
one molecule of potassium hydroxide, one aldehyde molecule being 
oxidised to the corresponding acid, and the other being reduced to a 
primary alcohol : 

2 C 6 H 5 . CHO + KOH = C 6 H 5 . CO . OK + C 6 H 5 . CH 2 . OH . 

Since the aldehydes are in part easily obtained, the different primary 
alcohols may be prepared advantageously by this reaction. Thus, 

/OCH3 /C 3 H r 

anisic alcohol p-C<.HZ and cuminic alcohol p-C 6 HZ 

x:h 2 . OH \CH 2 . OH 

are obtained by treating anisic aldehyde and cuminol, respectively, 
with alcoholic potash at the ordinary temperature or on heating. 
m-Nitrobenzylalcohol may also be obtained easily from m-nitrobenzal- 
dehyde and aqueous potash. The aldehyde of furfurane., furfurol, is 
converted under the same conditions into furfurane alcohol and pyro- 
mucic acid : 



2 H 



-r,CH 

+ H 2 = C 4 H 3 . CH 2 . OH + C 4 H 3 . CO . OH. 

v^ v^raw Furfurane alcohol Pyromucic acid 



O 

Furfurol 



The primary aromatic alcohols behave in all respects like the corre- 
sponding aliphatic alcohols in forming ethers and esters, e.g. : 



C G H 5 . CH 2 . 
C 6 H 5 .CH/ 


C 6 H 5 . CH 2 ^ 
CH/ 




CH 3 .CO.OCH 2 .C 6 H 5 


Benzyl ether 


Benzylmethyl ether 


Aceticbenzyl ester 



276 SPECIAL PART 

On oxidation they are converted first into aldehydes and finally into 
acids : 

C 6 H 5 . CH 2 . OH + O = C 6 H 5 , CHO + H 2 0, 

C G H 5 . CH 2 . OH + 2 = C G H 5 . COOH + H 2 0. 



26. REACTION: CONDENSATION OF AN ALDEHYDE BY POTASSIUM 
CYANIDE TO A BENZOIN 

Example : Benzoin from Benzaldehyde x 

Mix 10 grammes of benzaldehyde with 20 grammes of alcohol 
and treat the mixture with a solution of 2 grammes of potassium 
cyanide and 5 c.c. of water. Boil on the water-bath for one hour 
(reflux condenser). The hot solution is poured into a beaker 
and allowed to cool slowly ; the crystals separating out are filtered 
off, washed with alcohol, and dried on the water-bath. For con- 
version into benzil (see next preparation), they need not be re- 
crystallised. In order to obtain perfectly pure benzoin, a small 
portion of the crude product is recrystallised from a little alcohol 
in a test-tube. Melting-point, 134 . Yield, about 90% of the 
theory. 

If an aromatic aldehyde of the type of benzaldehyde is warmed in 
alcohol solution with potassium cyanide, substances are obtained which 
possess the same composition, but with double the molecular weight of 
the aldehyde : 

C 6 H 5 .CO.CH-C 6 H 5 
2C 6 H 5 .CHO= I . 

OH 

Benzoin 

Since a small quantity of potassium cyanide has the power to con- 
dense large quantities of the aldehyde, the reaction may possibly take 
place as indicated by the equations below. In the first phase, one 
molecule of aldehyde reacts with one molecule of potassium cyanide : 



(1) C r H, 5 .CO |H + CN K = C fi H 5 .COK + HCN. 

Potassium benzaldehyde 

The hydrocyanic acid then reacts with a second molecule of alde- 



1 A. 198, 150. 



AROMATIC SERIES 277 

hyde, forming an addition-product, mandelic nitrile, in the second 

phase : 

C G H 5 .CH— CN 

(2) C G H 5 .CHO + HCN= I 

' ' OH 

Mandelic nitrile 

In the third phase a molecule of potassium benzaldehyde acts upon a 
molecule of the nitrile with the elimination of potassium cyanide, and 
the formation of the benzoin : 

C 6 H 5 . CH . CN C 6 H 5 . CO . CH . C c fL 5 

(3) C 6 H 5 .COK+ I = I +KCN. 

OH OH 

The molecule of potassium cyanide required for equation (1) is thus 
again formed, and may condense two more molecules of aldehyde, etc. 

In the same way from anisic aldehyde and cuminol, there are obtained 
aniso'in and cuminoi'n, respectively : 

/OCHo = CH3O . C e H 4 . CO . CH . C H 4 . OCH 3 
2P-QH/ " I 

\CHO OH 

Anisic aldehyde Aniso'in 

•C 3 H 7 = C 3 H 7 . C G H 4 . CO . CH — C 6 H 4 . C 3 H 7 . 
2P-C C H 4 < I 

x:ho oh 

Cuminol Cumino'in 

With potassium cyanide furfurol yields furoin : 

C 4 H 3 . CO . CH . C 4 H 3 
2 C 4 H 3 . CHO = I 

Furfurol OH 

Furoin 

Benzoin and its analogues are derivatives of the hydrocarbon di- 
benzyl, C 6 H 5 . CH 2 . CH 2 . C 6 H 5 , and in fact benzoin on reduction with 
hydriodic acid is converted into this hydrocarbon. 

The benzoins act, on the one hand, like ketones if the carbonyl 
group (CO) takes part in the reaction, and, on the other hand, like 
secondary alcohols if the group CH . OH (the secondary alcohol group) 
reacts. Thus they have the power to form oximes and hydrazones 
with hydroxylamine and phenyl hydrazine respectively. If benzoin is 
reduced with sodium amalgam, the ketone group is converted into the 
secondary alcohol group ■ 



278 



SPECIAL PART 

C e H 5 . CO . CH . C 6 H 5 C 6 H 5 . CH— CH . C 6 H 5 

I +H 2 = || 

OH OH OH 

Hydrobenzo'in 

If the reduction is effected by zinc and hydrochloric acid or glacial 
acetic acid, the carbonyl group is not attacked, but the alcohol group 
is reduced and desoxybenzo'in is obtained : 

C C H 5 . CO . CH . C C H 5 C 6 H 5 .CO.CH 2 .C 6 H 5 + H,0, 

I +H 2 = 

OH Desoxybenzo'in 

a compound of especial interest, because in it, as in acetacetic ester, one 
of the two hydrogen atoms of the methylene group (CH 2 ), in conse- 
quence of the acidifying influence of the adjoining negative carbonyl 
and phenyl groups, may be replaced by sodium ; with the sodium com- 
pound the same kind of syntheses may be effected as with acetacetic 
ester : 

C G H 5 . CO . CH . C 6 H 5 C 6 H 5 . CO . CH-C 6 H 5 

I +IC 2 H 5 = I +NaI. 

Na C 2 H 5 

Sodium desoxybenzo'in Ethyl desoxybenzo'in 

Benzoin, further, acts as an alcohol, the hydroxyl group being capa- 
ble of reacting with alkyl- and acid-radicals to form ethers and esters. 
If oxidizing agents act on benzoin, the alcohol group is oxidized to a 
ketone group, as is the case with all secondary alcohols : 

C 6 H 5 .CO.CH.C 6 H 5 -f O 

I = C d H 5 . CO . CO . C 6 H 5 + H 2 0. 

OH Dibenzoyl = Benzil 

The next preparation will deal with this reaction. 

27. REACTION: OXIDATION OF A BENZOIN TO A BENZIL 
Example : Benzil from Benzoin 

The crude benzoin obtained in the preceding preparation is 
finely pulverised after drying, and heated in an open flask, with 
frequent shaking, with twice its weight of pure concentrated nitric 
acid, for 1^-2 hours on a rapidly boiling water-bath. When the 
oxidation is ended, the reaction-mixture is poured into cold water ; 



AROMATIC SERIES 279 

after the mass solidifies the nitric acid is poured off; it is 
then washed several times with water, pressed out on a porous 
plate, and crystallised from alcohol. After filtering off the 
crystals separating out, they are dried in the air on several layers 
of filter-paper. Melting-point, 95 . Yield, about 90% of the 
theory. __ 

The equation representing the oxidation of benzoin to benzil has 
been given under the preceding preparation. The analogues of ben- 
zoin also give, on oxidation, compounds of the benzil series. Thus 
from anisoin and cumino'in, anisil and cuminil respectively are 
obtained : 

€H 3 . C 6 H 4 . CO . CO . C 6 H 4 .OCH 3 ; C 3 H 7 . C 6 H 4 . CO . CO . C 6 H 4 . C 3 H 7 . 

Anisil Cuminil 

Benzil acts like a ketone in that it forms oximes with hydroxylamine. 
The oximes are of exceptional interest, since our knowledge of the 
stereochemistry of nitrogen proceeds from them. Benzil forms two 
monoximes and three dioximes. The constitution of these compounds 
will be discussed later, under the preparation of benzophenone-oxime. 

On fusion with potassium hydroxide or by long heating with a water 
solution of potassium hydroxide, benzil undergoes a remarkable change, 
in that by taking up water it passes over to the so-called benzilic acid : 

C 6 H 5 .CO.CO.C 6 H s + H 2 = 3 ^C.CO.OH. 

C 6 H/| 

OH 

Diphenylglycolic acid = 
Benzilic acid 

Anisil and cuminil also yield, in a similar way, anisilic and cuminilic 
acids. 

28. REACTION: THE ADDITION OF HYDROCYANIC ACID TO AN 
ALDEHYDE 

Example : Mandelic Acid from Benzaldehyde 1 

(a) Mandelic Nitrile 

In a flask containing 13 grammes of finely pulverised 100% 
potassium cyanide, or an equivalent amount of the purest salt 

1 B. 14, 235 



280 SPECIAL PART 

available, pour 20 grammes of freshly distilled benzaldehyde, and 
add to this from a separating funnel, the flask being cooled with 
ice, a quantity of the most concentrated hydrochloric acid, corre- 
sponding to 7 grammes of anhydrous hydrochloric acid (about 20 
grammes concentrated acid), drop by drop, with frequent shaking. 
The reaction-mixture is then allowed to stand, with frequent shak- 
ing, for one hour, then poured into about 5 volumes of water, the 
oil washed with water several times, and finally separated in a 
dropping funnel. Owing to the ease with which the nitriles 
decompose, a further purification is not possible. Yield, almost 
quantitative. 

Much better results are obtained by preparing mandelic nitrile 1 
thus : Pour 50 c.c. of a concentrated solution of sodium bisulphite 
over 15 grammes of benzaldehyde in a beaker ; stir the mixture 

/ H 

with a glass rod until the addition product C 6 H 5 .C — OH 

\sO3Na 
solidifies to a pasty mass. It is then filtered with suction, pressed 
firmly together, and washed once with a little water. The double 
compound is stirred up with water to a thick paste, and treated 
with a cold solution of 12 grammes potassium cyanide in 25 
grammes of water. After a short time, very easily on stirring, the 
crystals go into solution, and the nitrile appears as an oil, which is 
separated from the solution in a dropping funnel. 

(b) Saponification of the Nitrile 

The nitrile is mixed with four times its volume of concentrated 
hydrochloric acid in a porcelain dish, and evaporated on the 
water-bath until crystals begin to separate out on the upper surface 
of the liquid. 

The reaction-mixture is then allowed to stand over night in a 
cool place; the crystals separating out, are triturated with a little 
water, filtered off with suction, and then washed with not too 
much water. A further quantity of the acid may be obtained by 



1 Ch. Z. 1896, 90. 



AROMATIC SERIES 28 1 

extracting the filtrate with ether ; after evaporating off the ether, 
the residue is heated in a watch-crystal some time on a water- 
bath. The crude mandelic acid is pressed out on a porous plate, 
and is obtained pure by recrystallising it from benzene. Melting- 
point, n8°. Yield, about 10-15 grammes. 

(c) Separation of the Inactive Mandelic Acid into its Active 
Components 1 

A mixture of 20 grammes of crystallised cinchonine, 10 grammes 
of crystallised mandelic acid, and 500 c.c. of water is heated 
with quite frequent shaking in an open flask for an hour on an 
actively boiling water-bath. After cooling, the portions undis- 
solved are filtered off, and are not washed. To this clear solution 
(a) add a few crystals of d-cinchonine mandelate (see below), and 
allow it to stand, according to the conditions, one or more days in 
a cool place (6-8° ; in summer in a refrigerator, in winter in a 
cellar if necessary). In order to purify the crude d-cinchonine 
mandelate separating out, it is filtered off (filtrate A), pressed out 
on a porous plate, and recrystallised from water, using for each 
gramme of the dried salt 25 c.c. of water (heating as above 
described for an hour, with quite frequent shaking, in an open 
flask upon a water-bath). On filtering the cold solution the un- 
dissolved portions remaining are not washed. If the solution be 
seeded with a few crystals of d-cinchonine mandelate and allowed 
to stand under the same conditions referred to above, a purer salt 
will crystallise out. To obtain the free dextro-mandelic acid the 
purified salt is dissolved in not too much water, and then treated 
with a slight excess of ammonia, which precipitates the chincho- 
nine ; this is filtered off, and, after recrystallisation from diluted 
alcohol, may be used for other experiments. The filtrate, which 
contains dextro-ammonium mandelate, is acidified with hydro- 
chloric acid and extracted with ether. If the residue obtained on 
evaporating the ether be heated in a watch-glass some time on a 
water-bath, then, on cooling, crystals of dextro-mandelic acid 



1 B. 16, 1773 ; 32, 2385. 



282 SPECIAL PART 

separate out ; they are pressed out on a porous plate and recrys- 
tallised from benzene. Melting-point, 133-134 . 

The pure lsevo-mandelic cannot be obtained readily from small 
quantities of mandelic acid ; but a preparation showing to a slight 
extent lsevo-rotatory power may be obtained in the following way : 
The nitrate A is worked up for the free acid exactly as in the 
method described for pure dextro-cinchonine mandelate ; since a 
portion of the d-modification has been removed from the solution, 
it should be laevo-rotatory. 

From the three preparations thus obtained, viz. inactive mandelic 
acid, the pure d-acid, and the impure 1-acid, water solutions of the 
proper concentration are prepared, and their properties investi- 
gated by a polariscope (consult text-books on Physics). 

If one is not in possession of d-cinchonine mandelate for the 
first experiment, a proper seeding material is prepared as follows : 
To a few cubic centimetres of solution (a) obtained above is added, 
drop by drop, a saturated solution of salt until a slight precipita- 
tion takes place. The solution is now heated until the precipitate 
redissolves, and is allowed to stand until crystals separate out, 
which may require several days. The crystals thus obtained are 
those of cinchonine hydrochloride upon which small quantities of 
d-cinchonine mandelate have been deposited ; the latter are in 
sufficient quantity, however, to cause a further separating out of 
the d-salt. 

Hydrocyanic acid unites with aromatic as well as aliphatic aldehydes 
and ketones with the formation of a-oxyacid nitriles : 





/OH 
= CH 3 .CH< 


CH3.CHO + HCN 




Aldehydecyanhydrine 




a-lactic nitrile 




QH5V /OH 


C 2 H 5 .CO.C 2 H 5 +HCN 


Diethylketone 


Diethylglycolic nitrile 




/OH 
= C C H 5 .CH< 

x:n 


C 6 H 5 .CHO + HCN 


Benzaldehyde 


Mandelic nitrile 



AROMATIC SERIES 283 

•OH 



QH, . CO . CH 3 + HCN = >C\ 

CH 3 / \CN 

Acetophenone Acetophenonecyanhydrine 

This reaction also takes place with more complex compounds con- 
taining the carbonyl group : 

CH 3 . CO . CH 2 . CO . OC 2 H s + HCN = CH 3 . C— CH 2 . CO . OC 2 H 5 



Acetacetic ester 


OH CN 


CHo.CO.CO.OH + HCN 


= CH 3 .C— CO.OH 


Pyroracemic acid 


OH CN 




a-Cyan-a-lactic acid 


C 6 H 5 .CO.CH 2 .OH + HCN 


= C,H,.C— CH 9 .OH 


Benzoylcarbinol 


OH CN 



The reaction may be effected by digestion with already prepared 
hydrocyanic acid at ordinary or higher temperatures, but in most cases 
it is more advantageous to employ nascent hydrocyanic acid as above. 

If the second method be followed, — treating the aldehyde with 
sodium bisulphite, — the reaction takes place in accordance with the 
following equation : 

X)H .OH 

C 6 H 3 . CH = C 6 H 5 . CH + KNaS0 3 

CN N:n 



SO,Na + K 



If the oxynitriles are subjected to saponification, for example, by 
boiling with hydrochloric acid, the free oxyacid is obtained, e.g. : 

/OH /OH 

C 6 H 5 .CH< +2H 9 + HC1 = C 6 H 6 .CH< + NH 4 C1 

x:n x:o. oh 

Mandelic nitrile Mandelic acid 

Since the cyanhydrine reaction takes place smoothly in most cases, 
it is frequently used for the preparation of a-oxyacids. 

Thus in the sugar group the cyanhydrine reaction is of extreme im- 
portance, not only for its value in determining constitution, but also for 
the syntheses of sugars or sugar-like substances containing long chains 
of carbon atoms. 

In reference to the latter, one example may be mentioned. If hydro- 



284 SPECIAL PART 

cyanic acid is united with grape sugar, which is an aldehyde, there is 
first obtained an oxynitrile, which on saponification yields an oxyacid. 
If this, or rather the inner anhydride (lactone) into which it easily 
passes, is reduced, the carboxyl group is reduced to an aldehyde group, 
and there is thus obtained a sugar containing one more secondary 
alcohol (CHOH) group than the original grape sugar: 

CN CO.OH 

CHO I I CHO 

I CH.OH CH.OH I 

(CH.OH) 4 + HCN= I saponified-^- I reduced ->-(CH.OH) 5 

I (CH.OH) 4 (CH.OH) 4 I 

CH 2 .OH I I CH 2 .OH 

CH 2 .OH CH 2 .OH 

Aldoheptose 

With the substance thus obtained a similar reaction may be carried 
out, and so on. 

Mandelic acid belongs to the class of substances containing an 
asymmetric carbon atom, i.e., one which* is in combination with four 
different substituents : n u 

SOH 
XX). OH 

Like all compounds of this class, it exists in two different space 
modifications, which bear the same relation to each other as does an 
object and its image, and owing to their power of revolving the plane 
of polarisation, are called dextro- and laevo-mandelic acids. The acid 
obtained in the above synthesis is optically inactive ; since, in the 
synthesis of compounds with an asymmetric carbon atom from inactive 
substances, an equal number of molecules of the dextro- and laevo- 
varieties are always obtained, which, in the above case, unite to form 
the inactive, so-called, para-mandelic acid. But, by different methods, 
the active acids can be obtained from the inactive modifications. If, 
e.g., the cinchonine salt of para-mandelic acid is allowed to crystallise, 
the more difficultly soluble salt of the dextro-acid separates out first, 
and then, later, the laevo-salt crystallises. By treatment with acids, the 
free active acids may be obtained. 

With the aid of certain micro-organisms, the inactive compounds 
may be decomposed into their active constituents. If, e.g., the well- 
known Penicillmm glaucum is allowed to grow in a solution of ammo- 
nium para-mandelate, it destroys the laevo-modification ; while another 
organism, Saccharomyces ellipsoideus, consumes the dextro-modification, 
and leaves the other. 



AROMATIC SERIES 285 

29. REACTION: PERKIN'S SYNTHESIS OF CINNAMIC ACIDi 

Example : Cinnamic Acid from Benzaldehyde and Acetic Acid 

A mixture of 20 grammes of benzaldehyde, 30 grammes of 
acetic anhydride, both freshly distilled, and 10 grammes of anhy- 
drous pulverised sodium acetate (for the preparation, see page 
127), is heated in a flask provided with a wide vertical air-con- 
denser about 60 cm. long, for 8 hours, in an oil-bath at 180 . 
If the experiment cannot be completed in one day, a calcium 
chloride tube is placed in the upper end of the condenser over 
night. After the reaction is complete, the hot reaction-product 
is poured into a large flask ; add water, and then distil with steam, 
until no more benzaldehyde passes over. The quantity of water 
used here is large enough so that all of the cinnamic acid dissolves 
except a small portion of an oily impurity. The solution is then 
boiled a short time, with some animal charcoal, and filtered ; on 
cooling, the cinnamic acid separates out in lustrous leaves. Should 
it not possess the correct melting-point, it is recrystallised from hot 
water. Melting-point, 133 . Yield, about 15 grammes. 

The reaction involved in the Perkin synthesis takes place in accord- 
ance with this equation : 

C G H 5 . CHO + CH 3 . CO . ONa = C 6 H 5 . CH=CH . CO . ONa + H 2 0. 

Sodium cinnamate 

The reaction, however, does not take place, as appears from the 
equation, by the direct union of the aldehyde-oxygen atom with the 
hydrogen atoms of the methyl group and a combination of the resulting 
residues, but it proceeds in two phases. 

In the first, the sodium acetate unites with the aldehyde, forming 
sodium phenyl lactate : 

C 6 H 5 .CH.CH 2 .CO.ONa. 
(1) C 6 H 5 .CHO + CHo.CO.ONa= J | 

OH 

Sodium phenyl lactate 



1 J- z ^77, 7 8 9 I B. 10, 68 ; 16, 1436 ; A. 227, 48. 



286 SPECIAL PART 

In the second phase, this salt, under the influence of acetic anhydride, 
loses water, upon which the sodium cinnamate is formed : 

(2) C 6 H 5 .CH.CH 9 .CO.ONa 

| = C 6 H 5 . CH=CH . CO . ONa + H 2 0. 

OH 

That sodium acetate, and not the acetic anhydride, condenses with 
the benzaldehyde, is proved by the following facts : If, instead of sodium 
acetate, sodium proprionate is used, and this is heated with benzalde- 
hyde and acetic anhydride, cinnamic acid is not obtained, but methyl 
cinnamic acid : 

C 6 H 5 . CH— CH— CO . ONa 
(i) C 6 H 5 .CHO + CH 3 .CH,.CO.ONa = | | 

OH CH, 

(2) C 6 H 5 .CH— CH.CO.ONa C 6 H 5 .CH=C— CO. ONa + HX>. 

II = 1 

OH CH 3 CH 3 

Sodium methyl cinnamate 

It follows from this that the sodium salt used always takes part in 
the reaction. In the experiment it is of course necessary that the 
fusion is not carried out at so high a temperature as in the above 
example, but only at the heat of the water-bath ; at higher tempera- 
tures the sodium salt of proprionic acid and acetic anhydride decom- 
pose into sodium acetate and proprionic anhydride, so that cinnamic 
acid is obtained, and therefore, apparently, the anhydride reacts with 
the aldehyde. 

The Perkin reaction is capable of numerous modifications, since in 
place of benzaldehyde, its homologues, its nitro- and oxy-derivatives, 
etc., may be used. On the other hand, the homologues of sodium 
acetate may be used as has been pointed out. The condensation 
in these cases always takes place at the carbon atom adjoining the 
carboxyl group. Halogen substituted aliphatic acids will also react; 
thus from benzaldehyde and chloracetic acid, chlorcinnamic acid is 
obtained : 

C 6 H 5 . CHO + CH 2 . CI .CO . OH = C 6 H 5 . CH=CC1 . CO . OH + H 2 0. 

In place of the aliphatic homologues of acetic acid the aromatic sub- 
stituted acetic acids can also be used, e.g. : 



C fi H< . CHO + C.H, . CH, . CO . OH 



C 6 H 5 .CH=C— CO.OH, 



Phenyl acetic acid Phenyl cinnamic acid 



AROMATIC SERIES 287 

These examples are sufficient to show the wide application of the Per- 
kin reaction. 

A very similar reaction takes place on heating sodium acetate with 
the cheaper benzalchloride, instead of benzaldehyde : 

C G H, . CHC1 2 + CH 3 . CO . ONa = C 6 H 5 . CH=CH . CO . ONa + 2HCI. 

Cinnamic acid, its homologues and analogues, behave on the one 
hand like acids, since they form salts, esters, chlorides, amides, etc. 
Further, they show the properties of the ethylene series in that they 
take up by addition the most various kinds of atoms and groups. By 
the action of nascent hydrogen two atoms of hydrogen are added to 
the molecule of cinnamic acid with a change from double to single 
union : 

C 6 H 5 . CH=CH . CO . OH + H 2 = C 6 H 5 . CH 2 . CH 2 . CO . OH. 

Hydrocinnamic acid 

It also combines with chlorine and bromine : 

- Cl 2 = C e H 5 . CHC1 . CHC1 . CO . OH 

Dichlorhydrocinnamic acid 

Br 2 = C 6 H 5 . CHBr . CHBr . CO . OH. 

Dibromhydrocinnamic acid 

Further, it unites with hydrochloric, hydrobromic, and hydriodic 
acids, e.g. : 

C (i H 3 . CH=CH . CO . OH + HBr = C G H 5 . CHBr . CH 2 . CO . OH. 

jS-bromhydrocinnamic acid 

The halogen atom in these cases always unites with the carbon atom 
not adjoining the carboxyl group. 

Hypochlorous acid also unites with cinnamic acid with the forma- 
tion of phenylchlorlactic acid : 

C 6 H 5 . CHzzCH . CO . OH + ClOH 

OH 

The o-nitrocinnamic acid from which indigo is synthetically prepared 
is of technical importance. If cinnamic acid, or better, an ester of it, 
is nitrated, a mixture of the o- and p-nitroderivatives is obtained 
which can be separated into its constituents. If bromine is allowed to 
act on the o-nitrocinnamic acid, there is obtained : 



C 6 H 5 . CH— CHC1 . CO . OH. 



o-C G H 4 



/NO, 



\, 



CHBr— CHBr. CO. OH 



288 SPECIAL PART 

If this acid is boiled with alcoholic potash, two molecules of hydro- 
bromic acid are split off as in the preparation of acetylene from ethyl- 
ene bromide, and o-nitrophenylpropriolic acid is formed, which, with 
alkaline reducing agents, yields indigo, and is used in indigo printing : 

/N0 2 
o-C 6 H 4 < 

NCeeC.CO.OH. 

By the decomposition of an alkaloid found with cocaine, a stereo- 
isomeric cinnamic acid (allocinnamic acid) is obtained, which bears 
the same relation to cinnamic acid that maleic acid does to fumaric 
acid: 

C 6 H 5 .C.H C 6 H 5 .CH 

II II 

H.C.CO.OH HO.OC.CH. 

Cinnamic acid Allocinnamic acid 



30. REACTION: ADDITION OF HYDROGEN TO AN ETHYLENE 
DERIVATIVE 

Example : Hydrocinnamic Acid from Cinnamic Acid 

In a glass-stoppered cylinder, or a thick-walled preparation glass, 
treat 10 grammes of cinnamic acid with 75 c.c. of water; add a 
very dilute solution of caustic soda until the acid passes into solu- 
tion and the liquid is just alkaline. If a precipitate of sodium 
cinnamate separates out at this point, too much caustic soda has 
been used. It is then treated gradually with about 200 grammes 
of 2 % sodium amalgam, and heated gently, as soon as this has 
become liquid, on the water-bath for a short time. The liquid is 
then decanted from the mercury and acidified with hydrochloric 
acid, upon which the hydrocinnamic acid separates out as an oil ; 
when cooled with ice-water and rubbed with a glass rod, it solidifies 
to a crystalline mass. After pressing it out on a porous plate, the 
acid is recrystallised from water. Since it possesses a low melting- 
point, it may separate out as an oil on cooling, in which case pro- 
ceed according to the directions given on page 8. Melting-point, 
47 . Yield, 8-9 grammes. 

The equation for the reaction has been given under cinnamic acid. 
The same reaction also takes place on heating with hydriodic acid and 
red phosphorus. The acid does not show any noteworthy reactions. 



AROMATIC SERIES 289 



31. REACTION: PREPARATION OF AN AROMATIC ACID-CHLORIDE 
FROM THE ACID AND PHOSPHORUS PENTACHLORIDE 

Example : Benzoyl Chloride from Benzoic Acid 1 

Treat 50 grammes of benzoic acid in a dry J-litre flask, with 90 
grammes of finely pulverised phosphorus pentachloride under the 
hood ; the two are shaken well together, upon which, after a short 
time, reaction takes place with energetic evolution of hydrochloric 
acid, and the mass becomes liquid. In order to prevent the 
vessel, which has become strongly heated by the reaction, from 
cracking, it is not placed on the cold stone floor of the hood, but 
on a wooden block or straw ring. After standing a short time, 
the completely liquid mixture is twice fractionated (under the 
hood) with the use of an air condenser, observing the directions 
given on pages 24 and 25. Boiling-point of benzoyl chloride, 200 . 
Yield, 90 % of the theory. 

The formation of benzoyl chloride takes place in accordance with 
the following reaction : 

C 6 H 5 . CO . OH + PCI,- = C e H 5 . CO . CI + POCl 3 4- HC1 

It has been mentioned under acetyl chloride that, for the preparation 
of the aromatic acid-chlorides, phosphorus pentachloride is generally 
used. Benzoyl chloride differs from acetyl chloride in that it is more 
difficultly decomposed by water. 

Experiment : Treat J c.c. of benzoyl chloride with 5 c.c. of 
water and shake. While acetyl chloride, under these conditions, 
decomposes violently, the benzoyl chloride is scarcely changed. 
It is then warmed somewhat. It must be subjected to a longer 
heating before all the oil has been decomposed. 

In other respects, benzoyl chloride is a wholly normal acid-chloride, 
and what was said under acetyl chloride is applicable to this chloride ; 
only it is possible to prepare aromatic amides by a different method 
from that used for the preparation of acetamide. 

Experiment : In a porcelain dish, 10 grammes of finely pulver- 
ised ammonium carbonate are treated with 5 grammes of benzoyl 

1 A. 3, 262. Ostwald's Klassiker der exakten Wissenschaften, Nr. 22. (Investi- 
gations concerning the Radical of Benzoic Acid, by Wohler and Liebig.) 
u 



29O SPECIAL PART 

chloride ; they are intimately mixed with a glass rod and heated 
on the water-bath until the odour of the acid-chloride has van- 
ished. The mixture is then diluted with water, filtered with suction, 
washed with water, and crystallised from water. Melting-point of 
benzamide, 12 8°. 

C 6 H 5 . CO . CI + NH 3 = C 6 H 5 . CO . NH 2 + HC1 

Since the aromatic amides are generally insoluble in water, they are 
usually prepared by the method just given, and not, as in the case of 
acetamide, by heating the ammonium salt of the acid. 



32. REACTION: THE SCHOTTEN-BAUMANN REACTION FOR THE 
RECOGNITION OF COMPOUNDS CONTAINING THE AMIDO-, IMIDO-, 
OR HYDROXYL-GROUP 

Example : Benzoicphenyl Ester from Phenol and Benzoylchloride 1 

Dissolve a small quantity of crystallised phenol (about \ gramme) 
in 5 c.c. of water in a test-tube and add \ c.c. of benzoyl chloride ; 
make the solution alkaline with a solution of caustic soda and, with 
shaking, heat gently a short time over a free flame. If the reac- 
tion-mixture is cooled by water and then shaken and the sides of 
the tube rubbed with a glass rod, the oil separating out solidifies 
to colourless crystals, which are filtered off with suction, washed 
with water, pressed out on a porous plate, and recrystallised in a 
small test-tube from a little alcohol. Melting-point, 68-69 . 

As already mentioned under acetyl chloride, acid-chlorides react with 
alcohols, phenols, primary and secondary amines, the chlorine atom 
uniting with the hydrogen of the hydroxyl-, amido-, or imido-group, 
with the elimination of hydrochloric acid, while the residues combine 
to form an ester or a substituted amide. The value of the Schotten- 
Baumann reaction depends on the fact that this reaction is so essen- 
tially facilitated by the presence of sodium hydroxide or potassium 
hydroxide, that even in the presence of water the decomposition takes 
place, which in the absence of alkalies is not possible : 

C c H 5 .OH + C 6 H 5 .CO.Cl + NaOH=C 6 H 5 .O.OC.C 6 H 5 + NaCl + H 2 

1 B. 19, 3218; 21, 2744; 23, 2962; 17, 2545. 



AROMATIC SERIES 



291 



The reaction is of great importance, especially for the recognition and 
characterisation of soluble compounds containing the groups mentioned 
above. It is obvious that if it is desired to test even small quantities 
of those compounds, the most difficultly soluble acid derivatives of 
them must be prepared. The benzoyl derivatives are particularly well 
adapted to this purpose. A few examples may render this statement 
clearer: If a water solution of a poly-acid aliphatic alcohol, e.g., 
glycerol, or of the various sugars, from which the dissolved substance 
will only separate with difficulty, is treated with benzoyl chloride and 
alkali, a benzoate is formed, which is generally insoluble in water, and 
which can be recognised by its melting-point. For the recognition of 
primary and secondary amines the method of procedure is the same. 
Thus, e.g., it is not difficult to convert aniline (one drop dissolved in 
water) by the above method to benzanilide, which can be recognised 
by its melting-point, 163 . (Try the experiment.) 



The soluble amido-phenols, di- and poly-amines are also converted 
into difficultly soluble benzoyl derivatives : 

/NH 2 /NH.CO.C fi H 5 

C 6 H 4 < + 2 C 6 H 5 . CO . CI = C 6 H 4 < + 2 HC1 

\OH \O.OC.C 6 H 5 

NH 9 /NH . CO . C fi H 3 

- + 2 C 6 H 5 . CO . CI = C 6 H / + 2 HC1. 

NH 2 \NH.CO.C G H 5 

In place of benzoyl chloride, other chlorides, e.g., phenylacetyl chloride, 
or benzenesulphon chloride, can be used, which act in a similar way. 
Acetyl derivatives may also be prepared in the presence of alkalies in 
water solution, only in this case acetic anhydride and not the easily 
decomposed acetyl chloride is used. At times the reaction takes place 
better by using potassium hydroxide in place of sodium hydroxide. 



292 SPECIAL PART 



33. REACTION: (a) FRIEDEL AND CRAFTS' KETONE SYNTHESIS i 
(b) PREPARATION OF AN OXIME 
0) BECKMANN'S TRANSFORMATION OF AN OXIME 

Example : Benzophenone from Benzoylchloride, Benzene and 
Aluminium Chloride 

(a) To a mixture of 30 grammes of benzene, 30 grammes of 
benzoyl chloride, and 100 c.c. (= 130 grammes) of carbon disul- 
phide in a dry flask, add, in the course of about 10 minutes, with 
frequent shaking, 30 grammes of freshly prepared and finely pulver- 
ised aluminium chloride, which is weighed in a dry test-tube closed 
by a cork. The flask is then connected with a long reflux con- 
denser, and heated on a gently boiling water-bath until only small 
amounts of hydrochloric acid are evolved : this will require about 
2-3 hours. The carbon disulphide is then distilled off, and the 
residue, while still warm, is carefully poured into a large flask 
containing 300 c.c. of water and small pieces of ice. The residue 
adhering to the walls of the first flask is treated with water, and 
the water added to the main quantity. After the reaction-mixture 
has been treated with 10 c.c. of concentrated hydrochloric acid, 
steam is passed into it for about a quarter-hour. The residue 
remaining in the flask is, after cooling, extracted with ether, the 
ethereal solution washed several times with water, filtered, and 
shaken up with dilute caustic soda solution. After drying with 
calcium chloride, the ether is evaporated, and the residue distilled 
from a fractionating flask, the side-tube of which is as near as pos- 
sible to the bulb. Boiling-point, 29 7 . Melting-point, 48 . Yield, 
about 30 grammes. 

{I?) A solution of 2 grammes of benzophenone in 15 c.c. of al- 
cohol is, with cooling, treated with a cold solution of 1.5 grammes 
of hydroxylamine hydrochloride in 5 c.c. of water, and 3.5 
grammes of caustic potash in 6 grammes of water; the mixture 
is heated two hours on the water-bath, with a reflux condenser. 
Then add 50 c.c. of water, and filter off, if necessary, any un- 

1 A. ch. [6] i, 518. 



AROMATIC SERIES 293 

changed ketone which balls together very easily on shaking ; 
acidify the filtrate slightly with dilute sulphuric acid, and recrys- 
tallise the free oxime from alcohol. Melting-point, 140 . 

(V) A weighed amount of the oxime is dissolved in some 
anhydrous, alcohol-free ether, at the ordinary temperature, and 
gradually treated with i|- times its weight of finely pulverised 
phosphorus pentachloride. The ether is then distilled off, the 
residue, with cooling, is treated with water, and the precipitate 
separating out is recrystallised from alcohol. Melting-point, 163 . 

(a) If an aromatic or an aliphatic acid-chloride is allowed to act on 
an aromatic hydrocarbon in the presence of an anhydrous aluminium 
chloride, one of the benzene-hydrogen atoms will be replaced by an 
acid radical, a ketone being formed : 

C G H G + C G H 5 . CO . CI = C G H 5 . CO . C G H, + HC1 

Diphenyl ketone 
=Benzophenone 

C G H G + CH, . CO . CI = C G H - . CO . CH, + HC1. 

Phenylmethyl ketone 
=Acetophenone 

The reaction may be varied if (1) in place of benzene a homologue is 

used: 

CH 
CTT.CH, + C G H 5 .CO.Cl = p-C c H 4 / + HC1. 

x CO . CH 3 

Toluene Phenyltolyl ketone 

In cases of this kind, the acid-radical always enters the para position 
to the alkyl radical. If this is already occupied, it then goes to the 
ortho position. (2) In place of hydrocarbons, phenol-ethers, which 
react with extreme ease, can be used : 

X)CH.> 
C G H 5 .OCH 3 + C G H 5 .CO.Cl = C G H 4 < + HC1. 

x:o . c g h, 

Anisol Anisylphenyl ketone 

Concerning the entrance of the acid-radical, the statements made above 
are also true for this case. (3) In place of benzoyl chloride or acetyl 



/CH 3 
C G H C + C G H 4 < =C ( .H 5 .C0.C C H 4 .CH S + HC1 

\co.ci 

Toluyl chloride 



294 SPECIAL PART 

C 6 H 6 + CH 3 . CH 2 . CO . CI = C 6 H 5 . CO . CH 2 . CH 3 + HC1 
C 6 H 6 + C 6 H 5 . CH 2 . CO . CI = C 6 H 5 . CO . CH 2 . C 6 H 5 + HC1. 

Phenylacetyl chloride Phenylbenzyl ketone = 

desoxybenzoi'n 

In this way, starting from o- or m-toluic acid, the o- or m-tolyl- 
phenyl ketone can be prepared ; it cannot be obtained by the action of 
benzoyl chloride on toluene. (4) Substituted acid-chlorides like 
brombenzoyl chloride, nitrobenzoyl chloride, etc., can be used, and 
thus halogen or nitroketones are obtained : 



C H 6 + C 6 H 4 </ = C 6 H 5 . CO . C 6 H 4 . Br + HC1 

CO . CI Brombenzophenone 

Brombenzoyl chloride 

/N0 2 
C G H 6 + C 6 H 4 ^ = C 6 H 5 .CO.C 6 H 4 .N0 2 + HC1. ? 

CO . CI Nitrobenzophenone 

Nitrobenzoyl chloride 

(5) Finally, the chlorides of dibasic acids react with the formation of 
diketones or ketonic acids : 

CH 2 — CO . CI CH 9 . CO . C 6 H 5 

I + 2 C 6 H 6 =-| + 2 HC1 

CH 2 — CO . CI CH 2 . CO . C 6 H 5 

Succinic chloride 

.CO. CI /CO.C 6 H 5 

m- and p-C 6 H 4 < + 2 C 6 H 6 = C 6 H 4 < + 2 HC1 

x:o.ci \CO.C 6 H 5 

Iso- and tere-phthalyl chloride 

/C i 

CO +2 C 6 H 6 = C 6 H 5 . CO . C 6 H 5 + 2 HC1. 

N:i 

Phosgene Benzophenone 

In these reactions if but one chlorine atom should react, the chlorides 
of the three following acids would be obtained : 



CH 2 .CO.C 6 H 5 

1 
CH 2 .CO.OH 


/CO.C c H 3 
C 6 H 4 < 

x:o.oh 


C 6 H 5 .CO.OH. 

Benzoic acid 


enzoylproprionic acid 


Benzoylbenzoic acid 





AROMATIC SERIES 295 

From the chloride of phthalic acid phthalophenone is formed, im- 
portant on account of its relation to the fluorescein dyes : 

C 6 H 5\ / C 6 H 5 



C 6 H 4 < >0 + 2 C 6 H 6 = C 6 H 4 / No + 2 HC1. 
x CO X CO / 

Phthalophenone 

Michler's ketone, tetramethyldiamidobenzophenone is of technical 
importance ; it is obtained from dimethyl aniline and phosgene, and is 
used in the preparation of dyes of the fuchsine series (see Crystal 
Violet) : 

/ C 6 H 4 .N(CH 3 ) 2 

2 C C H 5 . N(CH 3 ) 2 + COCl 2 = CO +2 HC1. 

\C 6 H 4 .N(CH 3 ) 2 

The Friedel-Crafts reaction can also be used for the preparation of 
the homologous aromatic hydrocarbons, since in place of the acid- 
chloride, halogen alkyls may be caused to act on the hydrocarbons : x 

C 6 H 6 + C 2 H-Br = C 6 H 5 .C 2 H 5 + HBr 

/CH 3 
C 6 H 5 . CH 3 + CH 3 C1 = C C H 4 < + HC1. 

\CH 3 

Toluene Xylene 

But in this connection the reaction is in many cases, and indeed in 
the simplest case, not of equal importance with its application for the 
ketone syntheses, for three reasons : First, the product of the reaction 
is a hydrocarbon which can again react ; thus it is often difficult to 
limit the reaction to the desired point. For example, in the action of 
methyl chloride on toluene, not only is one hydrogen atom substituted, 
with the formation of dimethyl benzene, but varying quantities of tri-, 
tetra-, penta-, and hexa-methyl benzene are also formed. A second 
disadvantage is this: In the different series a mixture of isomers is 
obtained; in the above case, e.g., not only one of the three dimethyl 
benzenes, but a mixture of the o-, m-, and p-varieties is formed, which 
cannot be separated like the homologues by fractional distillation. 
The reaction is still further complicated in that the aluminium chloride 
partially splits off the alkyl groups : 

HC1 = C«H« + CH,C1. 



1 B. 14, 2627. 



296 



SPECIAL PART 



Since the lower homologues thus formed again react synthetically with 
the halogen alkyls, and the halogen alkyls on elimination also take part 
in the reaction, mixtures often difficult to separate are formed. In 
some favourable cases the reaction is of use in the preparation of the 
homologues of benzene. The reaction is also applicable to aromatic 
chlorides which contain the halogen in the side-chain : 

C fi H 5 . CH 2 . CI + C 6 H 6 = C G H 3 . CH 2 . C 6 H 5 + HC1 

Benzyl chloride Diphenyl methane 

N0 2 .C G H 4 .CH 2 .C1 + C 6 H 6 = N0 2 .C 6 H 4 .CH 2 .C fi H, + HC1. 

Nitrodiphenyl methane 

As the chlorides of dibasic acids yield diketones, the alkylene chlorides 
or bromides, as well as tri- and tetra-halogen substituted hydrocarbons, 
can react with several hydrocarbon molecules, e.g. : 



2CH,+ CH 9 Br 



3 C 6 H 6 + CHC1 3 



Chloroform 



C 6 H 5 .CH 2 . CH 2 . C (! H 5 + 2 HBr 

Dibenzyl = 
s-Diphenyl ethane 

CH.(C 6 H 5 ) 3 + 3 HC1 

Triphenyl methane 



4C c H 6 + CHBr 2 — CHBr 2 

Acetylene tetrabromide 



C 6 H 5 

I 
CH 

! 

C 6 H 5 



C,H 3 

I 
•CH +4 HBr. 

I 

C 6 H 5 



s-Tetraphenyl ethane 

In the latter reaction, anthracene is also formed, according to the 
equation : 



4 HBr. 





Br 


\ / 
CH 

1 
CH 

/ \ 


Br 




/ CH \ 

Anthracene 


H 2 + 


Br 




4- H 2 C C H 4 : 




Br 





For the synthesis of aromatic acids the Friedel-Crafts reaction is also 
of value, although the acids themselves are not directly obtained, but 
derivatives of them, which upon saponification yield the free acid, e.g. : 

C 6 H 6 + CI . CO . NH 2 = C H 5 . CO . NH 2 + HC1, 



Urea chloride 



Benzamide 



AROMATIC SERIES 297 

C 6 H 6 + C 6 H 5 .NCO =C 6 H 5 .CO.NH.C 6 H s 

Phenyl cyanate Benzanilide 

C 6 H 6 + C 6 H S .NCS =C 6 H 5 .CS.NH.C 6 H 5 . 

Phenyl mustard oil Thiobenzanilide 

The last two reactions are to be considered as cases of the normal 
Friedel-Crafts reaction, since the cyanate and mustard oil unite in the 
first phase with hydrochlorid acid, forming an acid-chloride, which then 
reacts with the hydrocarbon with elimination of hydrochloric acid, e.g. : 

/NH.C 6 H 5 
C,H..NCO + HCl = CO 

\ci 

Phenyl carbamine chloride 

If one considers that in the modifications, in place of the hydro- 
carbons, ethers, mono- and poly-acid phenols, naphthalene, thiophene, 
diphenyl, naphthol-ethers, and many other compounds can be used, the 
great value of the Friedel-Crafts reaction will be readily understood. 

Concerning the role which aluminium chloride plays in the reaction, 
it is still not perfectly clear ; certain it is that hydrocarbons as well as 
phenol-ethers unite with it to form double compounds which are of 
assistance in causing the reaction to take place. 

(b) By the action of hydroxylamine on aldehydes and ketones, 
oximes 1 (aldoximes, ketoximes) are formed in accordance with the 
following typical reactions : 

C 6 H 5 . CHO + NH 2 . OH = C 6 H 5 . CH=N . OH + H 2 

Benzaldoxime 

C fi H 3 .C.C 6 H 5 

C 6 H 5 .CO.C G H 5 + NH.,.OH = N + H,0. 

I 
OH 

Benzophenone oxime 

Oximes may be obtained by three methods: (1) The alcoholic 
solution of the aldehyde or ketone may be treated, generally, with a 
concentrated water solution of hydroxylamine hydrochloride and the 
mixture allowed to stand at the ordinary temperature, or it may be 
heated in a flask provided with a reflux condenser, or in a bomb-tube. 
An addition of a few drops of concentrated hydrochloric acid often 



1 B. 15, 1324. 



298 SPECIAL PART 

expedites the reaction. (2) The formation of oximes may be brought 
about by the use of free hydroxylamine obtained by treating its hydro- 
chloride with the theoretical amount of a solution of sodium carbonate. 
(3) Oximes may in many cases be very easily obtained, if, as above, 
for one carbonyl group three molecules of hydroxylamine hydro- 
chloride and nine molecules of potassium hydroxide are used ; in the 
presence of a large excess of hydroxylamine in a strongly alkaline 
solution, generally a very smooth decomposition takes place. Since 
the oximes possess a weak acid character, under these conditions the 
alkali salt of the oxime is first obtained, e.g. : 

C 6 H 5 .C.C 6 H 5 

N 

I 
OK 

from which the free oxime is liberated by treating it with an acid. 

Of especial significance for the stereo-chemistry of nitrogen are the 
oximes of aldehydes as well as those of the unsymmetrical ketones. 
By the action of hydroxylamine on benzaldehyde, e.g., there is formed 
not only a single oxime, but a mixture of two stereo-isomers. This is 
also true when oximes are formed from many unsymmetrical ketones. 
The existence of these isomers is explained by the assumption that 
the three valencies of nitrogen do not lie in a plane, but that they 
extend into space, proceeding from a point like the three edges of a 
regular triangular pyramid. 1 Since, e.g., in the formation of benzald- 
oxime, the hydroxyl-group of the hydroxylamine is vicinal to either 
the phenyl-group or hydrogen atom, the two following stereo-isomers 
are possible : 

QH 5 .C.H C 6 H 5 .C.H 

II and || 

HO— N N— OH 

OH vicinal to C 6 H 5 OH vicinal to H 

The stereoisomeric forms of an unsymmetrical ketone are, according to 
this conception, to be expressed by the following formulae, e.g. : 

BrC (; H 4 .C.C H 5 BrC 6 H 4 .C.C 6 H 5 

and 
HO— N N— OH 

OH vicinal to C 6 H 4 Br OH vicinal to C 6 H 5 



1 B. 23, II, 1243. 



AROMATIC SERIES 299 

With symmetrical ketones it is obviously immaterial upon which of 
the two similar sides the hydroxyl-group finds itself, so that here only 
one oxime is possible. 

In this place the two mono-oximes and three dioximes of benzil may 
be referred to again. These compounds gave the impetus to the 
investigations x of this class of compounds. They are explained by 
the following space-formulae : 

C (i H 5 . C . CO . C G H 5 C 6 H 5 . C . CO . C 6 H 5 

II and || 

HO— N N— OH 

C 6 H 5 .C.C.C 6 H 5 C 6 H 5 .C C.C 6 H 5 C 6 H 5 .C C.C fi H 5 

II II ,11 II II II 

HO— N N— OH HO— N HO— N N— OH HO— N 

Not all aldehydes and unsymmetrical ketones yield two oximes. In 
many cases one form is so unstable (labile) that only the other 
(stabile) modification exists. 

(c) If phosphorus pentachloride is allowed to act on an oxime, it 
is transformed into an anilide, 2 e.g. : 

C 6 H 5 . C . C 6 H- 

II 
N = C 6 H 5 .NH.CO.C 6 H 5 

Benzanilide 

OH 

Benzophenone oxime 

This so-called Beckmann transformation has been of great significance 
for the explanation of the constitution of the isomeric oximes. If, e.g., 
phosphorus pentachloride is allowed to act on both of the above 
formulated stereoisomeric oximes of the brombenzophenone, the same 
compounds are not obtained from both, but two different ones, which, 
as follows from their saponification products, correspond on the one 
hand to the benzoyl derivative of bromaniline, and, on the other, to 
the brombenzoyl derivative of aniline : 

C 6 H 5 . CO . NH . C 6 H 4 . Br and BrC 6 H 4 . CO . NH . C 6 H 5 

The transformation takes place, probably, in the following way : If 
phosphorus pentachloride is allowed to act on an oxime, the hydroxyl- 
group is replaced by chlorine : 



1 B. 16, 503; 2i, 784, 1304, 3510; 22, 537, 564, 1985, 1996. 
3 B. 19, 988 ; 20, 1507 and 2580 ; A. 252, 1. 



300 SPECIAL PART 

C G H 5 . C . C G H 5 C G H 5 . C . C G H 5 

II-. II 

N +PC1 5 = N +HCI + POCI3 

OH CI 

But a compound of this kind, in which chlorine is united with nitrogen, 
is unstable, and it is immediately transformed into a more stable imido- 
chloride, the chlorine atom being replaced by a phenyl-group : 

C e H 5 . C . C e H 5 C 6 H 5 . C . CI 

II II 

N — >- N 

I I 

CI C G H 5 

Imidochloride of Benzanilide 
(Compare p. 134) 

If this is now treated with water, benzanilide is formed, in accord- 
ance with the following equation : 

C G H 5 . C . CI = N . C 6 H 5 + H,0 = C 6 H 5 . CO . NH . C G H 5 + HC1 

If the oxime of brombenzophenone, formulated above, is subjected 
to a similar reaction, the unstable chlorides are first obtained : 

Br . C 6 H 4 . C . C 6 H 5 Br . C G H 4 . C . C 6 H 5 

II and || 

CI— N N— CI 

Cl vicinal to C 6 H 4 Br CI vicinal to C 6 H 5 

If the most probable assumption is now made, that the chlorine 
atom gives up its position to the vicinal hydrocarbon radical, there are 
formed : 

C1.C.C,H, Br.C r H 4 .C.Cl 

II and 4 || 

Br.C G H 4 .N N.C C H 5 

from which, by treatment with water, there are obtained : 

Br . C G H 4 . NH . CO . C G H 5 and Br . C G H 4 . CO . NH . C G H 5 

Benzoyl bromanilide Brombenzoyl anilide 

Upon saponification, these yield : 
Br.C G H 4 .NH 2 + C G H 5 .CO.OH and Br. C G H 4 . CO . OH + C G H 5 NH 2 

Bromaniline Benzoic acid Brombenzoic acid aniline 



AROMATIC SERIES 3OI 

That hydrocarbon radical which in the oxime was vicinal to the 
hydroxyl-group, is, therefore, on saponification of the polymerised 
product, obtained in the form of a primary amine. In this way, the 
constitution of the stereoisomeric oximes of the unsymmetrical ketones 
is determined. 

Whatever may be the space configuration of the stereoisomeric al- 
doximes, the derivatives containing an acid radical (acetyl derivative) 
of the one form easily yield an acid-nitrile on being treated with soda, 
while the other two forms do not. The hypothesis proposed, which 
seems very probable, suggests that in the first case the acid radical (or 
in the corresponding oxime) the hydroxyl-group is vicinal to the alde- 
hyde hydrogen atom, while in the second case it is vicinal to the hydro- 
carbon residue : 



C„H,.C 



N, 



H 
OH 



Owing to the nearness of the C 6 H- . C . H Yields no 
oxygen and hydroxyl, it loses II nitrile. 

water easily, and yields a ni- 



Syn-Oxime ^ C ^ Q = N _ Anti-Oxime 



34. REACTION: REDUCTION OF A KETONE TO A HYDROCARBON 

Example : Diphenyl Methane from Benzophenone 1 

A mixture of 10 grammes of benzophenone, 12 grammes of 
hydriodic acid (boiling-point, 127 ), and 2 grammes of red phos- 
phorus is heated in a sealed tube 2 for 6 hours at 160 . The 
reaction-mixture is then treated with ether, poured into a small 
separating funnel, and shaken up with water several times. The 
ethereal solution is filtered through a small folded filter, and dried, 
the ether evaporated, and the residue distilled. Boiling-point, 
263 . On cooling, the diphenyl methane solidifies to crystals 
which melt at 27 . Yield, almost quantitative. 

Hydriodic acid, especially at high temperatures, is an extremely 
energetic reducing agent, which can be used to effect reduction when, 
as in the above case, another reducing agent, e.g., a metal and acid, 
could not be employed. The reducing action depends on the following 
decomposition : 

2HI = H 2 + I, 

1 B. 7, 1624. 2 Before opening the tube, see page 62. 



302 SPECIAL PART 

The above reaction takes place in accordance with the following 
equation : 

C 6 H 3 . CO . C 6 H 5 + 4 HI = C 6 H 5 . CH 2 .C 6 H 5 + H 2 + 2 I 2 

Diphenyl methane 

With the aid of hydriodic acid, not only ketones but also aldehydes 
and acids may be reduced to the hydrocarbon from which they are 
derived, e.g. : 

C 6 H 5 . CHO + 4 HI = C 6 H 5 .CH 3 + H 2 + 4 I 

Toluene 

C 6 H 5 . CO . OH + 6 HI = C 6 H 5 . CH 3 + 2 H 2 + 3 I 2 

Benzoic acid Toluene 

C 17 H 35 . CO . OH + 6 HI = C 18 H 38 + 2 H 2 + 3 I 2 

Stearic acid Octodecane 

Alcohols, iodides, etc., can also be reduced to their final reduction 
products, the hydrocarbons, e.g. : 

C 2 H 5 I -f HI = C 2 H 6 + I 2 

Ethyl iodide Ethane 

CH 2 .OH CH, 

I I 

CH . OH + 6HI = CH 2 + 3 H 2 + 3 I 2 

CH 2 . OH CH 3 

Glycerol Propane 

By heating with hydriodic acid, the unsaturated compounds take up 
hydrogen, eg. : 

C 6 H 6 + 6HI =C e H 12 + 3 I 2 

Hexahydrobenzene 

The effect of hydriodic acid is increased by the addition of red 
phosphorus. Under these conditions, during the course of the re- 
action, the liberated iodine unites with the phosphorus to form phos- 
phorus tri-iodide : 

3 I + P = PI 3 
which with the water present again decomposes to form hydriodic acid : 
PI, + 3H 2 6 = 3HI + P(OH), 

Phosphorous acid 

A definite amount of hydriodic acid can thus, provided a sufficient 
quantity of phosphorus is present, act as a continuous reducing agent. 



AROMATIC SERIES 



303 



35. REACTION: ALDEHYDE SYNTHESIS — GATTERM ANN-KOCH 

Example : p-Tolylaldehyde from Toluene and Carbon Monoxide l 

To 30 grammes of freshly distilled toluene (boiling-point no°) 
contained in a wide-necked vessel (an " extract of beef" jar is con- 
venient) cooled with water, add, not too quickly, 45 grammes of 
pulverised, freshly prepared aluminium chloride and 5 grammes 
pure cuprous chloride (see page 355). The vessel is closed by a 
three-hole cork ; in the middle hole is inserted a glass tube which 
carries a stirrer (paddle wheel of glass) ; the other holes are used 
for the inlet and outlet tubes (Fig. 75). 
After the apparatus has been fastened firm- 
ly in a clamp it is immersed into 
a casserole filled with water at 
20 . A current, not too rapid, of 
carbon monoxide and hydro- 
chloric acid gas is led in through 
the prong-shaped tube while the stirrer is 
set in motion (a small motor is convenient). 
The carbon monoxide, contained in a gas- 
ometer of about 10 litres, is passed first 
through a solution of caustic potash (1:1) 
and then through a wash-bottle containing 
concentrated sulphuric acid. The hydro- 
chloric acid is generated in a Kipp ap- 
paratus from fused ammonium chloride and 
concentrated sulphuric acid. It is passed FlG - 75- 

through a wash-bottle containing concentrated sulphuric acid. 
The gas currents are so regulated that the volume of the carbon 
monoxide is about twice as large as that of the hydrochloric acid. 
The escaping gas is led directly to the hood opening. In the 
course of an hour when about 1-2 litres of carbon monoxide have 
been passed into the mixture, the temperature rises to 25-30 ; 
the remainder of the gas is passed in during four to five hours. 

1 B. 30, 1622; 31, 1 149. 




304 



SPECIAL PART 



If the reaction-mixture should become so viscous before the lapse 
of this time that the stirrer revolves only with difficulty, the re- 
action may be stopped. The viscid product is then poured into 
a large flask containing crushed ice ; the aldehyde formed and 
any unattacked toluene is distilled over with steam. The distil- 
late — oil and water — is then shaken up with a sodium bisulphite 
solution for a long time. The toluene, remaining undissolved, is 
separated in a dropping funnel. If the aldehyde-bisulphite com- 
pound should crystallise out, water is added until it dissolves. The 
filtered water solution is then treated with anhydrous soda until it 
shows a decided alkaline reaction ; the aldehyde is then again 
distilled over with steam. It is extracted from the distillate with 
ether. Upon evaporating the ether, from 20-22 grammes of per- 
fectly pure tolylaldehyde remains. Boiling-point, 204 . 

Preparation of Carbon Monoxide 
In a round litre- flask heat 100 grammes of crystallised oxalic 

acid with 600 grammes of concentrated sulphuric acid. The gases 

evolved are passed into two 
large wash-cylinders (Fig. 74) 
filled with a solution of caus- 
tic potash (1 part caustic 
potash to 2 parts of water), 
and then into a gasometer 
(Fig. 76). At first the sul- 
phuric acid is heated some- 
what strongly. As soon as 
the oxalic acid has dissolved 
and a regular current of gas 
comes off, the flame is 
lowered. Before filling the 
gasometer the gas is tested 
1 by collecting a test-tube 
full over water and apply- 
ing a match. So long as 

air remains in the apparatus, a slight explosion will occur. But as 




AROMATIC SERIES 305 

soon as pure gas is evolved, it burns quietly in the tube. It is then 
admitted into the gasometer. When the evolution of gas ceases, 
the apparatus is taken apart. Since carbon monoxide is poisonous, 
the experiment is carried out under the hood, and care is taken 
not to breathe the gas. If it is desired to avoid the use of a 
gasometer, a regular and continuous current of carbon mon- 
oxide may be generated as follows : A litre flask, provided 
with a safety-tube, containing 200 grammes of oxalic acid and 200 
grammes of sulphuric acid (cone), is heated in an oil-bath to 
120 ; the temperature is gradually increased according to the 
conditions. If the gas be passed first into two caustic potash 
cylinders, and then into two sulphuric acid (cone.) cylinders, it 
may be used directly for the synthesis. 

A direct synthesis of the aromatic aldehydes by means of the Friedel- 
Crafts reaction could not be brought about until recently, because of 
the instability of formyl chloride, which, if formed, decomposes imme- 
diately into carbon monoxide and hydrochloric acid : 

H.CO.Cl = CO + HCl 

If it were stable, it should form aldehydes, in accordance with this 
equation : 



X . |H + C1| . CO . H = X . COH + HC1 

But now it is known that a mixture of carbon monoxide and hydro- 
chloric acid in the presence of cuprous chloride, which combines with 
the former, behaves like formyl chloride. 

The Gattermann-Koch synthesis may be expressed by the following 
equation : 

/CH 3 ch 3 

C 6 H 4 < ■ = C G H 4 < + HC1 

\ lH + Cl| .CO.H \COH 

From other hydrocarbons like o- and m-xylene, mesitylene, ethylben- 
zene, diphenyl, etc., in an analogous way, aldehydes may be obtained. 
As has been shown in the ketone syntheses, the acid radical goes into 
the para position to the alkyl residue, so also in the aldehyde syntheses 



306 SPECIAL PART 

the aldehyde group always enters the para position to the alkyl residue. 
Thus from toluene there is obtained : 



COH 



From o-xylene >- ( ] — CH 



COH 

ca 



From m-xylene 




CH 3 



I 
COH 



Since the Friedel-Crafts reaction, when applied to phenol ethers, yields 
the corresponding aldehydes far more easily than the same reaction 
applied to the hydrocarbons, it is remarkable that the Gattermann-Koch 
method cannot be used with phenol ethers. If it be desired to obtain 
aldehydes from them, hydrocyanic acid is used in place of carbon mon- 
oxide ; in these cases the presence of cuprous chloride is unnecessary. 
The action takes place, due to the union of hydrocyanic and hydro- 
chloric acids to form the chloride of imidoformic acid : 

/ H 
HCN + HC1 = C==NH 

\C1 

which, under the influence of aluminium chloride, reacts with the phenol 
ether, liberating hydrochloric acid : 

/OCHo /OCH 3 

C 6 H 4 < = C (; H 4 < + HC1 

\ |h + ci| .ch = nh \ch=nh 



AROMATIC SERIES 307 

There is thus obtained first the aldehyde-imide which, through the 
action of acids, passes over into the aldehyde with great ease : 

/OCH3 /OCH3 

C 6 H 4 < =NH 8 + C 6 H/ 

\CH = lNH + H 2 l Q \CHO 

In this way it is possible to introduce the aldehyde group into phenol 
ethers as well as into the phenols. The carbon monoxide is obtained 
in accordance with the following equation : 

COOH 

I = CO + CO, + H 9 

COOH 

The mixture of gases is separated by passing it through a solution of 
caustic soda or caustic potash ; the carbon dioxide is absorbed, and 
the carbon monoxide emerges in a pure condition. 



36. REACTION : SAPONIFICATION OF AN ACID-NITRILE 

Example : Toluic Acid from Tolyl Nitrile 1 

The p-tolyl nitrile obtained in Reaction 10 is heated with 
slightly diluted sulphuric acid on the sand-bath in a round flask 
with reflux condenser until crystals of toluic acid appear in the 
condenser. For each gramme of the nitrile a mixture of 6 
grammes of concentrated sulphuric acid with 2 grammes of water 
is used. After cooling it is diluted with water, the acid separating 
out is filtered off and washed several times with water. A small 
portion is dissolved in a little alcohol, and hot water added until 
the solution just becomes turbid • it is then boiled some time 
with animal charcoal. On cooling, the pure acid is obtained. 
Melting-point, 177 . Yield, 80-90% of the theory. 

By saponification in a narrow sense is understood the splitting up 
of an acid-ester into an alcohol and acid. It is, however, used in a 
wider sense to indicate the conversion of acid-derivatives, like nitriles, 
amides, substituted amides, e.g., anilides, into acids of the same name. 
Saponification may be conducted either in an alkaline or an acid solu- 
tion. Thus, for instance, acetamide reacts on heating with a solution 

1 A. 258, 10. 



308 SPECIAL PART 

of caustic potash or caustic soda with the formation of the alkali salt 
of acetic acid and the evolution of ammonia. Nitriles and esters may 
frequently be saponified by water solutions of the alkalies. Further, 
alcoholic caustic potash or caustic soda can be used for a similar pur- 
pose. Finally, saponification may be effected by heating with a sodium 
carbonate solution under pressure ; this method is especially well 
adapted for difficultly saponifiable amides or anilides. 

In order to effect saponification in acid solution, the substance to be 
saponified is heated with either hydrochloric acid or sulphuric acid in 
varying degrees of dilution, e.g. : 

3 3 /CH 3 

+ 2 H 2 Q = C 6 H 4 < + NH 3 

^CN \CO.OH 

p-Tolyl nitrile p-Toluic acid 

Acid amides may be easily saponified by dissolving in concentrated 
sulphuric acid, cooling, adding sodium nitrite, and then gradually 
heating, 1 e.g. : 

C 6 H 5 .CO.NH 2 + NOOH = C 6 H 5 .COOH + N 2 + H 2 
In order to saponify a nitrile by this method it is first converted by 
heating with 85 % sulphuric acid into the amide, and this is treated as 
directed above. 

Frequently it is better to allow the nitrite to act directly on the warm 
dilute sulphuric acid solution of the amide. 

The decomposition of the ethers of phenols is also designated as 
saponification. Such decomposition cannot be effected by the methods 
hitherto given. Hydriodic acid is used which, when heated with 
phenol-ethers, decomposes them into the phenol and the alkyl iodide : 

C 6 H 5 . OCH3 + HI = C 6 H 5 . OH + CH3I 

Anisol 

Anhydrous aluminium chloride may be used here with great advantage ; 
upon heating, it acts on the phenol-ether in the manner indicated by 
the following equation: 

3 C 6 H 5 . OCH3 + AICI3 = (C 6 H 5 . 0) 8 A1 + 3 CH 3 C1 

Aluminium salt 
of phenol 

If a phenol salt is treated with an acid, the free phenol will separate 
out. This method presents the advantage that it may be applied to 
substances containing, in addition to the phenol-ether radical, a redu- 
cible carbonyl group, which, if treated with hydriodic acid, would be 
changed. 

1 B. 26, Ref. 773; 28, Ref. 917; 32, 1118. 



AROMATIC SERIES 309 

37. REACTION: OXIDATION OF THE SIDE-CHAIN OF AN 
AROMATIC COMPOUND 

Example : Terephthalic Acid from p-Toluic Acid 

Dissolve 5 grammes of the crude toluic acid obtained in Reac- 
tion 36 in a solution of 3 grammes of sodium hydroxide in 250 c.c. 
of water ; heat in a porcelain dish on the water-bath, and gradually 
treat with a solution of 12 grammes of finely powdered potassium 
permanganate in 250 c.c. of water until, after long boiling, the red 
colour of the permanganate no longer vanishes. Alcohol is then 
added until the liquid is colourless, and, after cooling, the manga- 
nese dioxide separating out is filtered off; this is washed with hot 
water, and the nitrate, heated to boiling, is acidified with concen- 
trated hydrochloric acid. After cooling, the terephthalic acid is 
filtered off, washed with water, and dried on the water-bath. Yield, 
90 % of the theory. Terephthalic acid is insoluble in water. On 
heating, it sublimes without melting. 

It is a common property of aliphatic side-chains, united with the 
benzene nucleus, to pass over to carboxyl groups on oxidation. A 
methyl group requires 3 atoms of oxygen for oxidation : 

C fi H 5 . CH 3 + 30 = C 6 H 5 . CO . OH + H 2 

Toluene Benzoic acid 

If several side-chains are present in a compound, either all or a portion 
of them may be converted into carboxyl groups : 

/CH 3 

* C H 4< 

/CH 3 /* \C0 . OH 

C 6 H 4\ g ives 

\CH 3 \ /CO. OH 

C 6 H 4\ 

\CO.OH 



CeH 3 \-CH 3 

\CO . OH 

/CH 3 / /CH 3 

C 6 Hj£-CH 3 gives — ^QH^f CO.OH 
\CH 3 \ \CO . OH 

/CO. OH 

C 6 H 3 ^-CO.OH 

\CO.OH 



310 SPECIAL PART 

If a side-chain contains several carbon atoms, in many cases only 
the methyl group at the end of the chain can be oxidised, e.g. : 

X . CH 2 . CH 3 + 3 O = X . CH 2 . CO . OH + H 2 

But by an energetic oxidation all the carbon atoms, with the excep- 
tion of the last, are split off, e.g. : 

C 6 H 5 . CH 2 . CH 3 + 3 2 = C 6 H S . CO . OH + C0 2 + 2 H 2 

Ethyl benzene 

The basicity of the acid derived from the oxidation of a hydrocarbon 
accordingly gives an indication concerning the number of side-chains 
of the hydrocarbon. Derivatives of hydrocarbons are also capable of 
similar reaction, e.g. : 

/CH 3 /CO. OH 

C 6 H/ +30 = C 6 H 4 < + H 2 

NCI NCI 

Chlortoluene Chlorbenzoic acid 

/CH 3 /CO. OH 

C e H 4 < +30 = C 6 H 4 < + H 2 

NN0 2 \N0 2 

Nitrotoluene Nitrobenzoic acid 

CHo . CO . C G H 5 + 30 = C 6 H S . CO . COOH + H 2 

Acetophenone Phenyl glyoxylic acid 

The reaction carried out above takes place in accordance with this 
equation : 

/CHo /CO. OH 

C G H 4 < " + 3 = C 6 H/ +H 2 

NCO.OH NCO.OH 

Amines and phenols cannot be directly oxidised in most cases, but 
an indirect method must be employed, by which the former are con- 
verted into an acid derivative, and the latter into an ester. If, e.g., it is 
desired to convert p-toluidine into p-amidobenzoic acid, the base is first 
acetylated, and the acetatoluide is then oxidised : 

/CH 3 /CO. OH 

C G H 4 < + 3 = C G H 4 <( +H 2 

NNH . CO . CH 3 NNH . CO . CH 3 

The acid thus obtained is then saponified, and the desired amido- 
benzo'ic acid is formed : 



/CO. OH /NH„ 



C 6 H 4 <T +H 2 = C c H/ +CH3.CO.OH 

NNH.CO.CH, NCO.OH 



L 3 



AROMATIC SERIES 311 

If it is desired, on the other hand, to oxidise a phenol, e.g., cresol, 
/CH 3 
CqHa ? the sulphuric acid- or phosphoric acid-ester of it is first 

\OH 
prepared and oxidised ; the reaction-product is then saponified. As 
oxidising agent, dilute nitric acid (1 vol. cone, nitric acid to 3 vol. 
water 1 ), chromic acid or potassium permanganate is used. The mildest 
effect is obtained with the nitric acid, which is therefore used when all 
the side-chains are not to be oxidised, but only a portion of them, e.g. : 

/CH 3 XTH 3 

C 6 H 4\ >- C G H 4\ 

\CH 3 \CO.OH 

Nitric acid is also used in other cases, where, as frequently happens 
with ortho derivatives, other oxidising agents totally destroy the sub- 
stance. 

Chromic acid, in the form of its anhydride generally, dissolved in 
glacial acetic acid, or as a water solution of potassium dichromate or 
sodium dichromate acidified with dilute sulphuric acid, can also be 
used as an oxidising agent, not only in the case in hand, but also for 
the oxidation of alcohols, ketones, etc. In oxidation reactions, two 
molecules of chromic anhydride (Cr0 3 ) give three atoms of oxygen : 

2 Cr0 3 = C 2 3 + 3 O 

For the oxidation of aromatic hydrocarbons, 1 experience has shown 
that a good oxidising mixture is 40 parts of potassium dichromate, 
55 parts of concentrated sulphuric acid, diluted with twice its volume 
of water. 

With potassium permanganate 2 oxidation can be effected either in 
alkaline or in acid solution. In the first case, manganese dioxide is 
deposited : 

2 KMn0 4 + H 2 = 3 + 2 Mn0 2 + 2 KOH 

Two molecules of potassium permanganate yield, therefore, in alkaline 
solution, three atoms of oxygen. 

In acid solution (sulphuric acid), no manganese dioxide separates 
out, since it is dissolved by the sulphuric acid, with evolution of 
oxygen, to form manganous sulphate : 

2 KMn0 4 + 3 H 2 S0 4 = 50 + K 2 S0 4 + MnS0 4 + 3 H 2 

Two molecules of the permanganate in acid solution, therefore, yield 
5 atoms of available oxygen. 

In oxidising with potassium permanganate, a 2-5% solution is gen- 
erally used. An excess of the permanganate can be removed by the 
addition of alcohol or sulphurous acid. 

1 A - i33. 41 ; 137. 302- 2 B. 7, 1057. 



312 SPECIAL PART 



38. REACTION : SYNTHESIS OF OXYALDEHYDES. REIMER AND 

TIEMANN i 

Example : Salicylic Aldehyde from Phenol and Chloroform 

In a round litre flask dissolve So grammes of caustic soda 
in 8o c.c. of water by heating. Add 25 grammes of phenol ; 
cool the solution without shaking to 60-65 by immersion in cold 
water. By means of a two-hole cork attach to the flask an effective 
reflux condenser, and insert a thermometer the bulb of which dips 
into the liquid. Add 60 grammes of chloroform gradually, as fol- 
lows : At first add one-third through the condenser ; on gentle 
shaking the liquid becomes a fuchsine-red in colour. After a 
short time the colour changes to orange, and the temperature 
rises. When it reaches 70 the entire flask is immersed in cold 
water until the thermometer indicates 65 . In this way during 
the entire reaction the temperature is always kept between 65 
and 70 . Should it fall below 6o°, the mixture is warmed by im- 
mersing it a short time in hot water until the mercury rises to 65 °. 
After 10-15 minutes the second third of the chloroform is added, 
observing the precautions just given. Finally, after about 20 
minutes, the remainder of the chloroform is added. Since toward 
the end the reaction takes place very quietly, the flask is frequently 
immersed in hot water in order to maintain the temperature 
between the prescribed limits. The synthesis requires in all from 
i\ to 2 hours. Frequent shaking of the mixture, especially during 
the last phase, increases the yield materially. When the reaction 
is complete the chloroform is distilled off with steam. The orange- 
coloured alkaline liquid is allowed to cool somewhat, and is acidi- 
fied carefully with dilute sulphuric acid, upon which it becomes 
almost colourless ; finally, steam is passed into it until drops of oil 
no longer go over. 

The distillate is then extracted with ether, the ethereal solution 
separated from the water, and the ether evaporated. The residue, 
consisting of unchanged phenol and salicylic aldehyde, is treated 



1 B. 9, 423, 824; 10, 1562; 15, 2685, etc. 



AROMATIC SERIES 313 

with twice its volume of a concentrated solution of commercial 
sodium bisulphite. Upon stirring well for a long time with a glass 
rod, a solid paste of the double compound of the aldehyde and 
bisulphite should separate out. After standing from J-i hour the 
crystals are filtered with suction, pressed firmly together, and 
washed several times with alcohol to remove completely the ad- 
hering phenol, and finally with ether. The pearly, lustrous leaflets 
are then well pressed out on a porous plate and the aldehyde set 
free by a gentle warming with dilute sulphuric acid on the water- 
bath. On cooling, the mixture is extracted with ether, the ethereal 
solution dried over anhydrous Glauber's salt, the ether is evapo- 
rated, and the residue of the pure aldehyde is distilled. Boiling- 
point, 196 . Yield, 10-12 grammes. 

The small amount of the p-oxybenzaldehyde formed with the 
salicylic aldehyde is not volatile with steam, and remains back in 
the flask after the distillation with steam. In order to obtain it, 
the residue remaining in the flask after cooling is filtered through 
a folded filter, and the clear filtrate saturated with solid salt, upon 
which the p-oxybenzaldehyde separates out at once or on stand- 
ing. If this be filtered off, and the filtrate extracted with ether, 
a further quantity is obtained, which, together with the first, is 
purified by recrystallisation from water with the addition of a 
solution of sulphur dioxide. Melting-point, n 6°. Yield, 2-3 
grammes. 

The synthesis takes place in accordance with this equation : 

/ONa 
C G H 5 ONa + CHCI3 + 3 NaOH = C 6 H / + 3 NaCl + 2 H 

x CHO 

Probably the reaction takes place in the two phases : 



(1) 


/OH 
C r H/ 


/OH 
HCl + C,.H 4 < 

X CHC1 2 




' x H + CI CHC1 2 


(2) 


/OH 


/OH 
2 HCl + C 6 H / 

x CHO 


' X CH CI, + HJO 



314 SPECIAL PART 

By this method the aldehyde group may be introduced into mono- 
and poly-acid phenols ; it enters the ortho and para positions to a 
hydroxyl group : 

Phenol gives o- and p-oxybenzaldehyde, 

CH 3 CH 3 

o-Cresol >- and 

OHC\y \ycno 

CH, CH, 

OHO 

m-Cresol >- and 

; OH \/ 0H 

CHO 



p-Cresol >- only. 

OH 
OH 

Pyrocatechin >- j = Protocatechuic aldehyde. 

CHO 
OH OH 

Resorcin >- \ ; also a dialdehyde I 

V 0H \/ 0H 

CHO CHO 

OH 



/\.CH 



Hydroquinone >- \ Gentisin aldehyde. 

OH 

The reaction also takes place with the ethers of poly-acid phenols. 
Thus guaiacol gives : 

OH OH 

OHc/NoCHg J /\oCH 3 „ .... 
j 3 and | ° Vanillin. 

CHO 



AROMATIC SERIES 315 

From resorcinmonomethyl ether there are formed two monoalde- 
hydes and two dialdehydes. The reaction is also applicable to oxy- 
aldehydes as well as oxycarbonic acids. Thus from salicylic aldehyde 
there is formed a mixture of two oxyisophthalic aldehydes : 

/OH 

-CH( 

XTHO 

OH 
CHO 



p-oxybenzaldehyde gives : 

CHO 

That resorcin, in addition to a monoaldehyde, yields a dialdehyde, 
has always been mentioned. From the three oxybenzoic acids are 
formed two oxyaldehyde acids, 

/OH 
C 6 H 3 ^COOH 

x:ho 

This synthesis is capable of very wide application. But it has some 
defects. Thus the yield of aldehyde obtained in accordance with the 
original directions leaves much to be desired. The yield is very much 
decreased by the fact that a portion of the phenol does not enter into 
the reaction, and another portion reacts with the chloroform to produce 
an ester of ortho formic acid : 

3 C G H 5 ONa + CHCI3 = 3 NaCl + CH(OC 6 H 5 ) 3 

A portion of the aldehyde first formed is lost by condensation with 
some unattacked phenol, forming a derivative of triphenylmethane : 



/cho + 2h c,h 4 .oh 
c,h/ 



OH =H 2 + C^ 4 '° 

X H 



OH 



Further, a portion of the oxyaldehydes is converted into resins by 
the alkali. 

In addition, the separation of the mixture of the mono- and dialde- 
hydes is often attended with serious difficulty. 



3i6 



SPECIAL PART 



As already mentioned on page 306, the aldehyde group may be in- 
troduced into phenols by the use of condensation agents like aluminium 
chloride, zinc chloride, hydrocyanic and hydrochloric acids. These re- 
actions possess many advantages over those discussed above. They 
take place more smoothly, yield only the p-oxyaldehydes, and introduce 
only one aldehyde group ; further, only small amounts of resins are 
formed, and finally they may be applied to phenols like pyrogallol, 
phloroglucin, the two naphthols, poly-acid phenols of naphthalene, etc. 
With these substances the other reaction is useless. (See B. 19, 1765 ; 
32, 278, etc.) 



39. REACTION: KOLBE'S SYNTHESIS OF OXYACIDS 

Example : Salicylic Acid from Sodium Phenolate and 
Carbon Dioxide 1 

Dissolve 12J grammes of chemically pure sodium hydroxide in 
20 c.c. of water in a porcelain dish, or better a nickel dish, and 
with stirring, treat gradually with 30 grammes of crystallised phe- 
nol. The greatest portion of the water is then evaporated by 

heating over a free flame, 
the mass being continually 
stirred. As soon as a crys- 
talline film forms on the 
surface of the liquid, the 
heating is continued with 
a luminous flame, which is 
not placed directly under 
the dish, but is kept in con- 
stant motion. In order to 
fasten the dish, a pair of 
crucible tongs is clamped 
in a vertical position, and 
the dish supported between 
its jaws. There is first ob- 
tained a caked, bright-coloured mass, which is crushed from time 
to time with a mortar-pestle. As soon as the particles no longer 

1 J.pr. [2] 10,89; 27,39; 3L397- 




Fig. 77. 



AROMATIC SERIES 317 

bake together, the mass is pulverised quickly in a dry mortar, the 
dry mass is then heated with thorough stirring in a nickel dish to 
dusty dryness. It is then placed in a tubulated retort of 200 c.c. 
capacity. The retort is then immersed as far as possible in an oil- 
bath (Fig. 77). This is heated to no°, and at this temperature 
a current of dry carbon dioxide is passed over the sodium pheno- 
late (the end of the delivery tube is 1 cm. above the upper surface 
of the sodium phenolate) ; this is passed into the retort for an 
hour. The temperature is then gradually raised (20 per hour) 
during the course of four hours, while a not too rapid current is 
passed in, to 190 . The mixture is finally heated 1-2 hours at 
200 . During the operation the mass is stirred several times with 
a glass rod. After cooling, the phenol in the neck of the retort is 
melted by the application of a flame to the outside, the dusty, fine 
powder is poured into a large beaker, the retort is washed out 
several times with water, and the salicylic acid precipitated with 
much concentrated hydrochloric acid. After the reaction-mixture 
has been cooled with ice-water a long time, and the sides of the 
vessel rubbed with a glass rod, the crude salicylic acid is filtered 
off, washed with a little water, and pressed out on a porous plate. 

The purification of the crude salicylic acid is accomplished 
best with superheated steam. For this purpose the acid, in a dry 
condition, is placed in a short-necked flask, and heated in an oil- 
bath to 170 , a not too rapid current of steam at a temperature 
of 170-180 (see page 40) is passed over it. The connection 
between the flask and steam generator must not be made until 
the oil-bath and the steam have the same temperature. Since the 
acid distilling over very soon stops up a condenser tube of the 
usual width, one should use for this experiment a tube of 2.5 cm. 
width (width of mantel 5 cm., length of same 75 cm.). The 
connecting tube between the flask and condenser must be 2 cm. 
wide, and as short as possible. If the acid removed from the 
condenser be dissolved in the watery distillate in the receiver by 
heating, long colourless needles separate out on cooling. Melting- 
point, 1 5 6°. Yield, 5-10 grammes. 

The preparation of salicylic acid does not always take place 



318 SPECIAL PART 

successfully the first time. The success of the experiment depends 
particularly on the conditon of the sodium phenolate, which must 
be perfectly dry} If it " cakes " on heating the retort, there is 
great probability that the experiment will be unsuccessful. 

The operation should be so arranged that the sodium phenolate 
is prepared toward evening, so that it may be allowed to stand in 
a sulphuric acid desiccator over night. The drying in the current 
of carbon dioxide is begun immediately next morning. 

The synthesis is named after its discoverer, Kolbe. It takes place 
in three phases. In the first, the carbon dioxide is added to the 
sodium phenolate, which forms sodium phenyl carbonate : 

(I.) C 6 H 5 .ONa + C0 2 = C r H 5 .O.C0 2 Na 

In the above experiment this reaction is completed during the heat- 
ing up to uo° for one hour. In the second phase, the sodium phenyl 
carbonate is transformed into the so-called neutral sodium salicylate : 

/OH 
(II.) C 6 H 5 .O.C0 2 Na = C 6 H/ 

x C0 2 Na 

while in the last phase a molecule of this salt reacts with a molecule of 
unchanged sodium phenolate in the following way : 

/OH /ONa 

(III.) C 6 H/ +C 6 H 3 .ONa = C 6 H/ + C 6 H 5 .OH 

x CO . ONa x CO . ONa 

These two latter reactions take place during the gradual heating up 
to 20o°. Only one-half of the phenol, therefore, is converted into 
salicylic acid, the second half being obtained unchanged. 

A modification of the Kolbe synthesis which permits the immediate 
conversion of all the phenol into salicylic acid is known as Schmitt's 
synthesis. According to this method, as in the other, the sodium 
phenyl carbonate is first prepared ; this is then further heated in an 



1 The experiment is more certain of success if the sodium phenolate is heated 
a half hour in a current of dry hydrogen at 140 (retort in the oil-bath) before the 
introduction of the carbon dioxide; the mass must be cooled to no° before the 
latter is led in. 



AROMATIC SERIES 319 

autoclave under pressure to 140 , upon which it is completely trans- 
formed into sodium salicylate according to Equation II. Instead of 
preparing the sodium phenyl carbonate with gaseous carbon dioxide, 
the sodium phenolate may be mixed directly with liquid or solid carbon 
dioxide in the autoclave. 

The Kolbe synthesis is capable of very common application, since 
from each mon-acid phenol, a carbonic acid may be obtained in the 
same way as that used above. The carboxyl group under these condi- 
tions primarily seeks the ortho position to the hydroxyl group. The 
derivatives of phenols, e.g. the three chlorphenols, yield chlorinated 
salicylic acids. With acid-ethers of poly-acid phenols which still con- 

tain a free hydroxyl group, as, e.g., guaiacol, C G H 4 <^ , this reaction 

Ndh 

likewise takes place. From the two naphthols C 10 H 7 .OH the oxy- 

X)H 
naphthoic acids C 10 H 6 <f , can be obtained. 

XX). OH 

If in the Kolbe reaction instead of sodium phenolate, potassium 
phenolate is used, the para-oxybenzoic acid is obtained, and not the 
ortho-acid. The potassium phenolate, like the sodium phenolate, first 
absorbs carbon dioxide, and the potassium phenyl carbonate thus 
formed, heated in carbon dioxide up to 150 , also yields salicylic acid; 
but if the temperature is increased, an increasingly larger quantity of 
the para-acid is obtained, until finally at 220 the potassium para- 
oxybenzoate is the only product. 

The addition of carbon dioxide is effected with greater ease in poly- 
acid phenols. With these compounds the reaction begins if the phenol 
is boiled in a water-solution of ammonium carbonate or potassium 
hydrogen carbonate, e.g. : 



: e H 4\ 



OH /OH 

.- HO . CO . OK = C c H 3 ^-OH + H 2 
OH \C0.0K 



Salicylic acid is prepared technically on the large scale. Since it 
is an excellent antiseptic, it finds extensive application in preventing 
fermentation, for the preservation of meat, for the disinfection of 
wounds. It may easily be recognised, since its water solution gives 
a violet colour with ferric chloride ; in this action it differs from the 
para- and meta-modifi cations. It is volatile with steam ; for this rea- 
son it must not be boiled too long in an open vessel when it is to be 
recrystallised. All ortho-oxy carbonic acids show this property ; the 



320 SPECIAL PART 

meta- and para-isomers are not volatile with steam. If salicylic acid 
is heated strongly, it decomposes into carbon dioxide and phenol : 

/CO. OH 
C 6 H 4 < = C 6 H 5 .0H + C0 2 . 

X)H 

The para-oxycarbonic acids show the same property while the meta- 
acids are stable. 



40. REACTION: PREPARATION OF A DYE OF THE MALACHITE 
GREEN SERIES 

Example : Malachite Green from Benzaldehyde and Dimethyl- 
aniline 1 

(a) Preparation of the Leuco-base. — A mixture of 50 grammes 
of dimethylaniline and 20 grammes of benzaldehyde is heated 
in a porcelain dish, with frequent stirring, on the water-bath, for 
4 hours, with 20 grammes of zinc chloride, which has been pre- 
viously fused in a porcelain dish, and pulverised, after cooling. 
(See p. 324.) This viscous mass, which cannot be poured directly 
out of the dish, is melted by covering it with hot water, and 
heating it at the same time, on the water-bath ; while hot, it is 
transferred to a ^--litre flask. Steam is conducted into it, until no 
drops of it pass over. There is thus obtained the non-volatile 
leuco-base of the dye, in the form of a viscous mass, which adheres 
firmly to the walls of the distilling flask. After the liquid is cold, 
the water is poured off, the base adhering to the sides of the flask 
is washed with water several times, and then dissolved in the 
flask with alcohol, on the water-bath. After filtering, the solution 
is allowed to stand over night in a cool place, upon which the 
base separates out in colourless crystals ; these are filtered off, 
washed with alcohol, and dried in the air on several layers of 
filter-paper. By concentrating the mother-liquor, a second crys- 
tallisation may be obtained. Should the base not crystallise, but 
separate out in an oily condition, which frequently happens after 



1 A. 206, 83 ; 217, 250. 



AROMATIC SERIES 321 

a short standing of the filtered solution, this is due to the fact 
that an insufficient amount of alcohol has been used. In this 
case, more alcohol is added, and the mixture heated until the oil 
is dissolved. 

(b) Oxidation of the Leuco-base. — Dissolve 10 parts, by weight, 
of the completely dry leuco-base by heating in a quantity of 
dilute hydrochloric acid corresponding to 2.7 parts, by weight, 
of anhydrous hydrochloric acid. For the purpose, dilute pure 
concentrated hydrochloric acid with double its volume of water, 
determine the specific gravity of the diluted acid, and refer to a 
table to find out how much anhydrous acid the solution contains, 
and from this calculate how much of the solution must be taken 
in order to get the required amount of the anhydrous acid 
(2.7 grammes). The colourless solution of the leuco-base is 
then diluted in a large flask with 800 parts, by weight, of water, 
and treated with 10 parts of 40 % acetic acid (sp. gr. 1.0523), 
prepared by gradually diluting glacial acetic acid with water ; the 
mixture is well cooled by throwing in pieces of ice ; then, with 
frequent stirring, gradually add (during 5 min.) a quantity of 
freshly prepared lead peroxide paste corresponding to 7.5 grammes 
of pure lead peroxide. The peroxide is weighed off in a beaker, 
and treated with a quantity of water sufficient to form a very thin 
paste. The residue remaining in the beaker after the first empty- 
ing is washed out with water. After the addition of the peroxide, 
the reaction-mixture is allowed to stand five minutes, with frequent 
shaking; then add a solution of 10 parts of Glauber's salt and 
50 parts of water ; the solution is then filtered off through a folded 
filter from the precipitated lead sulphate and chloride. The filtrate 
is treated with a filtered solution of 8 parts of zinc chloride dis- 
solved in as small a quantity of water as possible ; then a saturated 
sodium chloride solution is added, until all the dye is precipitated. 
This is easily recognised by bringing a drop of the solution, with 
a glass rod on a piece of filter-paper ; a bluish green precipitate 
surrounded by a circle of a still fainter bright green colour will be 
formed. The precipitated dye is filtered off with suction, washed 
with a little saturated sodium chloride solution, and pressed out 

Y 



322 



SPECIAL PART 



on a porous plate. In order to purify it further, it may be dis- 
solved again in water ; and from the filtered solution, after cooling, 
it is again thrown out by sodium chloride. 

The reaction just carried out, discovered by Otto Fischer in 1877, is 
also used in the large scale for the preparation of Malachite Green, or 
Bitter Almond Green. In the formation of the leuco-base, the follow- 
ing reaction takes place : 

C 6 H 4 .N(CH 3 ) 2 = c /c 6 c h"-N(CH 3 ) 2 + H Q 



+ 



• C 6 H 4 .N(CH 3 ). 



Tetramethyldiamidotriphenylmethane 
= Leuco-base of Malachite Green 

The substance thus obtained is not a dye, but the reduction product 
of the real dye, which, on oxidation, passes over to the dye. Formerly, 
the dye formation was believed to take place in accordance with the 
following equation : 



/c'h 4 .n(ch 3 ). 



c< 



C 6 H 4 .N(CH 3 ) 2 



.H 



./ 



C fi H, 



CI 



H 



+ 



= C^C 6 H 4 .N(CH 3 ) 2 + H 2 0. 
X C 6 H 4 .N(CH 3 ) 2 C1 



The union, effected by the oxidation between the pentavalent nitrogen 
atom of the dimethyl aniline residue and the common methane-carbon 
atom, was considered to be the condition which determined the nature 
of the dye. At present, the view that the latter is determined by the 
presence of the quinone-like secondary benzene residue is generally 
accepted, and the formula of the dye-salt is written thus : 



<: 6 H 4 .N(CH 3 ) 2 
C 

HC/\CH 



HC 



CH 



= Quinoide formula of 
Malachite Green. 



CH/ I X 
CI 



CH, 



AROMATIC SERIES 323 

Further, it may be pointed out in this place that, in the formation of 
the leuco base, the hydrogen atom in the para position to the dimethyl- 
amido groups N(CH 3 ) 2 unites with the aldehyde oxygen atom to form 
water. The salt of the formula given above is difficult to separate 
from its solution. But if zinc chloride is added, a double salt of the 
same colour is formed : 

3(C 23 H 25 N 2 C1) + 2 ZnCl 2 + H 2 

which may be separated from its water solution by common salt. 

Malachite Green may also be made by a second method, which was 
discovered by Dobner : it consists in heating benzotrichloride with 
dimethyl aniline in the presence of zinc chloride : 



C< 



CI H 
CI + H 



/ 



C f? H 5 



C 6 H 4 .N(CH 3 ) 2 _ / C 6 H 4 .N(CH 3 ) 2 
C 6 H 4 .N(CH 3 ) 2 \<C 6 H 4 .N(CH 3 ) 2 + 2 HCL 
X C1 



Since the chlorine atom remaining over migrates toward a nitrogen 
atom, the dyestuff salt is directly formed by the transformation. Still, 
since the preparation of pure benzotrichloride on the large scale is diffi- 
cult, this method, which was formerly used, has been abandoned, and 
the dye is now prepared exclusively by Fischer's method. 

Malachite Green is a representative of a whole series of dyes, — the 
Malachite Green Series. If, instead of dimethyl aniline, diethyl aniline 
is used, an analogous substance, which bears the name of Brilliant 
Green, is formed. In place of benzaldehyde, substituted benzalde- 
hydes, etc., can be used. The dyes of the Bitter Almond Series colour 
only the animal fibres, silk and wool, directly. Vegetable fibre (cot- 
ton) is not coloured unless it has been previously mordanted. 



41. REACTION: CONDENSATION OF PHTHALIC ANHYDRIDE WITH 
A PHENOL TO FORM A PHTHALEIN 

Example : (a) Fluorescein. 1 (b) Bromination of Fluorescein 
with the Formation of Eosin 

(a) In a mortar grind up and intimately mix 15 grammes of 
phthalic anhydride with 22 grammes of resorcinol, and heat in an 



1 A. 183, 1. 



324 



SPECIAL PART 



oil-bath to 180 (Fig. 78). As a vessel for heating the mixture, 
an " extract of beef" jar, glazed inside, is well adapted to the 
purpose ; it can be obtained readily at a small cost, and may be 
used several times for the same fusion. It is suspended by its 
projecting edge from a triangle into the oil-bath. To the fused 

mass add, with stirring (glass rod), 
in the course of 10 minutes, 7 
grammes of pulverised zinc chlo- 
ride. This is prepared in the 
following way : 10 grammes of the 
commercial salt, which always con- 
tains water, is carefully heated to 
fusion over a free flame in a por- 
celain dish. After the mass has 
been kept in a fused condition for 
a few minutes, it is allowed to cool, 
and the solidified substance is re- 
moved from the dish with a knife 
and pulverised. After adding 7 
grammes of the anhydrous salt 
thus obtained, the temperature is 
increased to 210 , and the heating 
continued until the liquid, which 
gradually thickens, becomes solid, 
for which about 1-2 hours is required. The cold friable melt 
is removed from the crucible with a sharp instrument (it is best 
to use a chisel), finely pulverised, and boiled 10 minutes in a 
porcelain dish with 200 c.c. of water and 10 c.c. of concentrated 
hydrochloric acid. This causes the solution of the substance 
which did not enter into the reaction ; the addition of hydro- 
chloric acid is necessary to dissolve the zinc oxide and basic 
zinc chloride. The fluorescein is filtered from the solution, 
washed with water until the filtrate no longer gives an acid 
reaction ; it is then dried on the water-bath. Yield, almost 
quantitative. 

(b) Over 15 grammes of fluorescein in a flask, pour 60 grammes 




Fig. 78. 



AROMATIC SERIES 



325 



of alcohol (about 95 %), add, with frequent shaking, 33 grammes 
of bromine, drop by drop, from a separating funnel. This should 
require about a quarter-hour. In place of a separating funnel, it 
is advisable, as in all cases of bromination, to use a burette, by which 
the troublesome weighing of bromine is obviated. Since the spe- 
cific gravity of bromine at moderate temperatures is very nearly 3, 
it is only necessary to divide the required weight by 3, in order to 
find the number of cubic centimetres corresponding to the weight. 
Of the numerous kinds of burettes, the one best adapted to this 





Fig. 79. 



Fig. 80. 



purpose is the Winckler form ; since it possesses no cock, it can 
be inserted into the body of a flask with a not too narrow neck, 
and by this manipulation the disagreeable bromine vapours may 
be avoided (Fig. 79). In the above case, n c.c. of bromine 
are necessary. On the addition of bromine, it is observed that the 
quantity of fluorescein insoluble in alcohol steadily decreases, and 
that when about one-half of the bromine has been added, a clear, 
dark, reddish-brown solution is formed. This is due to the fact 
that the dibromide is first formed, which is easily soluble in 



326 SPECIAL PART 

alcohol. On the further addition of bromine, the tetra-bromide 
is formed, which, since it is difficultly soluble in alcohol, separates 
out in the form of brick-red leaflets. After all the bromine has 
been added, the reaction-mixture is allowed to stand for 2 hours, 
the precipitate is filtered off, washed several times with alcohol, 
and dried on the water-bath. The product thus obtained is a 
compound of 1 molecule of eosin and 1 molecule of alcohol. In 
order to obtain pure* eosin from it, the substance is heated a half- 
hour in an air-bath at 1 io° : during the heating, its colour becomes 
brighter. Since eosin is insoluble in water, the soluble potassium-, 
sodium-, or ammonium-salt is prepared on the large scale for dyeing. 
Ammonium Eosin. — Over a flat-bottom crystallising dish, \ 
filled with a concentrated ammonia solution, place a filter, of paper 
as strong as possible. Upon this is spread the eosin acid, in a 
layer about \ cm. thick, and the whole is covered with a funnel 
(Fig. 80). The bright-red crystals of the free eosin acid very 
soon assume a darker colour, and, after about three hours, it is com- 
pletely converted into the ammonium salt, which forms dark-red 
crystals with a greenish lustre. The end of the reaction is easily 
recognized, by testing a small portion with water. If it dissolves, 
the conversion is complete. 

On the large scale, this reaction is carried out in wooden chests 
containing a number of frames covered with coarse linen, arranged 
like drawers. After the eosin is spread out on the linen in thin layers, 
dry ammonia evolved from ammonium chloride and lime is passed into 
the chest, until a test-portion of the substance will completely dissolve. 

Sodium Eosin. — Grind 6 grammes of eosin with 1 gramme of 
dehydrated sodium carbonate, and in a not too small beaker 
moisten it with a little alcohol; after the addition of 5 c.c. of 
water, heat on the water-bath until the evolution of carbon dioxide 
ceases. To the water solution of sodium eosin thus obtained, add 
20 grammes of alcohol, heat to boiling, and filter the hot solution. 
On cooling, the soluble sodium salt separates out in the form of 
splendid, brownish-red needles of a metallic lustre. As is the 
case with many dyes, the crystallisation requires a long time ; one 
day, at least, is necessary. 



AROMATIC SERIES 



327 



Phthalic anhydride and phenols can react with each other in two 
different ways. (1) An equal number of molecules of each can con- 
dense, the oxygen atom of the anhydride, which unites the carbonyl 
groups, can combine with two ring-hydrogen atoms of the phenol to 
form one molecule of water ; this action results in the formation of an 
anthraquinone derivative : 



CO 
C 6 H 4 <; > 

<:o 



o + H, 



'CO 



.C 6 H 3 ,OH 



Phenol 



C 6 H 4 <^ co ^C 6 H 3 .OH 

Oxyanthraquinone 



Or (2) one molecule of the anhydride can react with two molecules of 
the phenol in such a way that one of the two carbonyl-oxygen atoms 
of the former combines with one ring-hydrogen of the two phenol 
molecules to form a so-called phthale'in : 



C 6 H 4 



[Hi 
CO + H 


.C 6 H 4 .OH 

.C 6 H 4 .OH 


HO OH 

1 1 
QH4 C G H 4 


CO 


= 


C 



CO 

Phenolphthalein= 
dioxyphthalophenone 

For the knowledge concerning this class of compounds, to which be- 
long numerous important dyestuffs, we are indebted to the investiga- 
tions of A. Baeyer (1871). Phthalophenone is considered to be the 
mother-substance of the group : 

/C 6 H 5 
/C\— C 6 H 5 

QH 4 / \o 

CO 

which, as already stated, is obtained from phthalyl chloride and benzene 
in the presence of aluminium chloride. If one conceives that the 
mother-substance can take up one molecule of water, a hypothetical 
mono-carbonic acid of triphenyl carbinol would result : 

/ C 6 H 5 

C >C 6 H 5 

^Sc 6 H 4 .CO.OH ? 
X)H 



328 



SPECIAL PART 



the formula of which shows very clearly the connection between the 
phthale'ins and the triphenyl methane derivatives. 

If, as expressed by the above equation, phthalic anhydride is allowed 
to act on phenol, phenolphthale'in is obtained, a substance of acid 
properties, colourless in the free condition ; its salts are red. It is 
used as an indicator in volumetric analysis. 

By the action of phthalic anhydride on resorcinol, the formation ot 
a tetraoxyphthalophenone would naturally be expected ; but fluorescein, 
containing the constituents of one molecule of water less than this, is 
obtained, an inner anhydride formation taking place between the two 
hydroxyl groups : 

.OH 



HO 



OH 



C 6 H 4 





H. 


C 6 H 3 < 
C«H 8 < 


/ 


o 1 




+ 


^OH 

x>]h 

X)H 


C 6 H 3<fy C G H 3 

= C 
C 6 H 4 0O 

CO 

Fluorescein 


,c 


o 


H. 


t< 


> 







+ 2H 2 0. 



Fluorescein is technically prepared on the large scale by the method 
given above. While phenolphthale'in, in spite of the intense colour 
of its salts, is not a dye, in that it does not colour fibres, fluorescein is 
a true dye which colours animal fibres a fast yellow. But it is not 
manufactured as a dye, since it has been replaced by other dyes that 
give as beautiful colours and are cheaper. A number of its halogen- 
and nitro-substitution products have valuable colouring properties, and 
are prepared from it. The simplest dye of this kind is eosin or tetra- 
brom-fluorescei'n, discovered in 1874 by Caro. The four bromine 
atoms are equally divided between the two resorcinol residues : 



HO 

I 



O 



OH 
i 



QHBr/ >C r HBr, 



C 
C 6 H 4 <^>0 
CO 



which follows from the fact that eosin in fusion with potassium hydrox- 
ide yields di-bromresorcinol besides phthalic acid. Instead of phthalic 
anhydride, the di- and tetra-chlor-substitution products are fused with 



AROMATIC SERIES 



329 



resorcinol on the large scale ; and so there is obtained in the phthalic 
acid residue, the di- and tetra-chlorfluoresce'ins from which halogen sub- 
stitution products, nitro-derivatives, ethers, etc., are prepared on the 
large scale (Phloxine, Rose Bengal). 

Besides fluorescein there is practically only one other phthalein 
prepared technically, Galle'in. This is done by heating phthalic anhy- 
dride with the ■zz-trioxybenzene — pyrogallol. In this case the same 
anhydride formation takes place as in the preparation of fluorescein, 
but there is a simultaneous splitting off of the hydrogen atoms of two 
hydroxyl groups resulting in a peroxide union : 



/CO 
C 6 H 4 <^ >0 



C— CJL 



OH 
— O 

01 
o 



Galle'in. 



XOH 



From galle'in, a derivative of anthracene, ccerulei'n, a new dye, is ob- 
tained by heating with sulphuric acid. Since 1887 the phthalei'ns have 
been on the market under the name of rhodamines, which are prepared 
in a manner similar to that of fluorescein, except that instead of 
resorcinol, m-amidophenol, or amidophenols substituted by alkyls in 
the amido-group, are used : 



C^ 

C e H\ >0 

CO 



H. 



II . 



/NH 9 
C 6 H 3 <( 


H 2 N NH 2 


"l ° 


[OH 

o]h 


C 6 H 3 <^>C 6 H 3 


^tt/ 


C +2 H 2 


c g h/ 

NH 2 


C 6 H 4 <^>0 




CO 




Simplest Rhodamine 



The rhodamine on the market is the tetra-ethyl derivative of this 
mother-substance . 



33° SPECIAL PART 



42. REACTION: CONDENSATION OF MICHLER'S KETONE WITH AN 
AMINE TO A DYE OF THE FUCHSINE SERIES 

Example : Crystal Violet from Michler's Ketone and Dimethyl 

Aniline 

A mixture of 25 grammes of dimethyl aniline, 10 grammes of 
Michler's ketone (this is on the market), and 10 grammes of 
phosphorus oxychloride, is heated in an open, dry flask, 5 hours, 
on an actively boiling water-bath. The blue-coloured mass is 
then poured into water, made alkaline with a solution of caustic 
soda, and treated with steam until no drops of the unattacked 
dimethyl aniline pass over. After cooling, the solidified colour- 
base remaining in the distillation flask is filtered from the alkaline 
solution, washed with water, and boiled with a mixture of 1 litre 
of water and 5 grammes of concentrated hydrochloric acid. The 
blue solution is filtered while hot from the colour-base, which 
remains undissolved ; the latter is boiled again with a fresh quan- 
tity of dilute hydrochloric acid ; this operation is repeated until 
the. substance has been almost entirely dissolved. After cooling, 
the solution of the dye is treated with finely pulverised salt 
(stirring) until the dye is precipitated. It is then filtered with 
suction, pressed out on a porous plate, and crystallised from a 
little water. On cooling, the Crystal Violet separates out in 
coarse crystals of a greenish colour ; these are filtered off and 
dried in the air on filter-paper. 

If Michler's ketone is heated with an amine in the presence of a 
condensation agent (phosphorus oxychloride, POCL), addition takes 
place, in accordance with the following equation : 

C 6 H 4 .N(CH 3 ) 2 C 6 H 4 .N(CH 3 ) 2 



CO + H.C 6 H 1 .N(CH 3 ) 2 =C<C : H,N(CH^ 

C e H 4 .N(CH 3 ) 2 OH 

Michler's ketone Hexamethylpararosaniline = 

Colour-base of Crystal Violet 



AROMATIC SERIES 



331 



If this is dissolved in hydrochloric acid, one molecule of this is added, 
and, as in the formation of Malachite Green, the elimination of a mole- 
cule of water immediately takes place and the dye is formed : 

,C 6 H 4 .N(CH 3 ) 2 



/C e H 4 .N(CH,)o 
C^-C e H 4 .N(CH 3 ) 2 

X: 6 H 4 .N(CH 3 ) 2 C1 



c 



\ 



c 

HC/\CH 



C 6 H 4 .N(CH 3 ) ; 



or 



HC 



c 



CH 



= Quino'ide formula. 



N 



Crystal Violet 

It is a derivative of parafuchsine 

/C 6 H 4 .NH 2 

C^C ( ,H 4 .NH 2 " 
C 6 H 4 .NH 2 C1 



./ 



C (i H 4 .NH 2 



C^-C H 4 .NH, 
^C (i H 4 =NH.,.Cl 



indeed, it may be considered as a hexamethyl parafuchsine. It is pre- 
pared technically in the same way, and forms the principal constituent 
of the Methyl Violet obtained by the oxidation of dimethyl aniline. 

Dyes can also be prepared in the same way by the combination of 
other amines with Michler's ketone, of which it is only possible to 
mention here Victoria Blue and Night Blue. 



43. REACTION: CONDENSATION OF PHTHALIC ANHYDRIDE WITH 
A PHENOL TO AN ANTHRAQUINONE DERIVATIVE 

Example : Quinizarin from Phthalic Anhydride and 
Hydroquinone 1 

A mixture of 5 grammes of pure hydroquinone and 20 grammes 
of phthalic anhydride is heated in an open flask with a mixture 
of 100 grammes of pure concentrated sulphuric acid and 10 



1 B. 6, 506 ; 8, 152 ; A. 212, 10. 



332 SPECIAL PART 

grammes of water for 3 hours in an oil-bath to 170-180 , and 
finally for 1 hour at 190-200 . The directions as to time and tem- 
perature must be followed as exactly as possible. The hot solution 
is poured, with stirring, into about 400 ex. of water in a porcelain 
dish, heated to boiling, and filtered hot with the aid of a Btichner 
funnel. The residue remaining on the filter is again boiled out 
with water and filtered while hot. In order to separate the quini- 
zarin from carbonaceous decomposition products, the precipitate 
is boiled with 200 ex. of glacial acetic acid, filtered hot with 
suction, the filtrate poured into a beaker, and, while hot, treated 
with its own volume of hot water. The residue remaining on the 
filter is again boiled up with 100 ex. glacial acetic acid, and, after 
filtering, treated as above. On cooling of the diluted acetic acid 
solution, the crude quinizarin separating out is filtered off, washed 
with water several times, dried first on the water-bath, and finally 
in an air-bath at 120 . Since it is difficult to obtain it pure by 
crystallisation, after drying it is distilled from a small retort of 
difficultly fusible glass, and is driven over as rapidly as possible 
with a large flame. A beaker is used as a receiver. After the 
distillate in the receiver and that in the neck of the retort (this 
is broken) has been finely pulverised, it is crystallised from glacial 
acetic acid, from which, on cooling, the quinizarin separates out 
in the form of large, orange-yellow leaves ; these are filtered off 
and washed with glacial acetic acid, which is steadily diluted with 
water, until finally only pure water is used. 

Under the preparation of fluorescein, it has already been mentioned 
that phthalic anhydride condenses with phenols in certain proportions, 
to form derivatives of anthraquinone. The reaction just effected takes 
place in accordance with the following equation : 

,ccx : /ccx 



C 6 H/ No + H 2 . C 6 H 2 . (OH) 2 = C 6 H/ \c 6 H a (OH) s + H 2 0. 
\co/' ' X CCK 



Quinizarin 

In an analogous way, mono-acid- as well as poly-acid phenols, combine 
with phthalic anhydride. It is of theoretical importance that from 
pyrocatechol (o-dioxybenzene), besides a second isomer, alizarin is 



AROMATIC SERIES 333 

obtained, showing that the two hydroxyl groups in alizarin are in the 
ortho position to each other. Of practical significance is the above 
reaction for the preparation of anthragallol, which is obtained on the 
large scale by heating pyrogallol with phthalic anhydride : 



-CO^ 



/" U \ 



C C H/ ^ |0 + H 2 | .C 6 H.(0H) 3 = C G H/ >C H.(OH) 3 + H 2 O. 



COv 



Pyrogallol Trioxyanthraquinone = 

Anthragallol 

It may be mentioned briefly that by the condensation of benzoic 
acid with oxybenzo'ic acids, similar compounds are also obtained : 



CO!OH H 



tt/ + \c,H.rOH)., = C ; H/ >( 



>C 6 H.(OH) 3 = C 6 HX >C (J H.(OH) 3 + 2H 2 0. 



H HO CO/ XC0/ 



Benzoic acid Gallic acid Anthragallol 

Quinizarin dissolves, like oxyanthraquinones, in alkalies with a 
violet colouration. (Try it.) Since it does not contain the hydroxyl 
groups in the vicinal a-/3-positions, it will not form dyes with metallic- 
salt mordants. This will be explained further under Alizarin. 



44. REACTION: ALIZARIN FROM SODIUM (3-ANTHRAQUINONE- 

MONOSULPHONATE 1 

Iii an autoclave or an iron pipe with a cap which can be 
screwed on (see page 64), heat a- mixture of 10 parts commercial 
sodium anthraquinonemonosulphonate, 30 parts of sodium hy- 
droxide, 1.8 parts of finely pulverised potassium chlorate, with 40 
parts of water, for 20 hours to 170 . After cooling, the melt is 
boiled out with water several times, and acidified at the boiling- 
point of the solution in a large dish with concentrated hydro- 
chloric acid. The alizarin separating out is then filtered off 
according to the quantity, either with suction or with the aid of 
a filter-press, washed with water, pressed out on a porous plate, 
and dried in an air-bath at 120 . In order to obtain it com- 
pletely pure, it is distilled rapidly from a small retort, and is 



1 A. Spl. 7, 300 ; B. 3, 359 ; 9, 281. 



334 SPECIAL PART 

crystallised from glacial acetic acid, or in large quantities from 
nitrobenzene. 

The sodium hydroxide fusion of the sodium anthraquinonemono- 
sulphonate is an abnormal reaction to the extent that besides the re- 
placement of the sulphonic acid group by hydroxyl, a hydrogen atom 
is also oxidised to a hydroxyl group : 



/C(X /H 

A >C 6 H 2 < +3NaOH 

\CO/ \SO„Na 



/CO\ /ONa 

= C 6 H 4 < >C 6 H 9 < + Na 9 S0 3 + 2 H 2 . 

\CO/ \ONa 

The tendency to the formation of alizarin is so great that even with- 
out the addition of an oxidising agent (potassium chlorate or nitrate), 
it is formed with the evolution of hydrogen. Formerly the oxygen of 
the air was used as the oxidising agent, the reaction being effected in air. 

In order to prepare alizarin on the large scale, anthracene is the 
starting-point ; this is obtained from the highest-boiling fractions of 
coal tar (anthracene oil). It is oxidised by chromic acid to anthra- 
quinone (see below), and this on heating with sulphuric acid is con- 
verted into the monosulphuric acid. The separation of this latter 
compound is greatly facilitated by the fact that it forms a sodium salt 
difficultly soluble in water, which, on account of its silvery appearance, 
is called " Silver salt." If the sulphonation mixture is diluted with 
water and neutralised with sodium carbonate, the sodium anthraquinone- 
monosulphonate is precipitated directly, which thus obviates the neces- 
sity of removing the excess of sulphuric acid beforehand. On the large 
scale the alizarin fusion is conducted exactly as on the small scale, 
except that autoclaves, with stirring attachments, are used. The con- 
stitutional formula of alizarin is : 



CO 




OH 



CO 



The salts are intensely coloured. The red aluminium salt, the 
violet ferric salt, and the garnet-brown chromic salt are especially im- 
portant in dyeing. With alizarin and all its related compounds the 
dyeing is effected by mordanting the fibre with a salt of one of the 



AROMATIC SERIES 335 

three oxides just mentioned; the thus prepared fibre is heated with 
a thin dilute water-paste of the free insoluble dye, whereby salts are 
formed on the fibre (Lakes). 

Of the numerous di- and poly-oxyanthraquinones only those are 
actual dyes which contain, like alizarin, two hydroxyl groups in the 
vicinal a-/?-position, i.e. the derivatives of alizarin (Rule of Liebermann 
and Kostanecki) . The above prepared quinizarin dissolves in alkalies 
with a violet colouration, but with metallic oxides it forms no salts on 
fibres. 

From two disulphonic acids of anthraquinone, two trioxyanthra- 
quinones, flavo- and anthra-purpurin, are prepared in a manner analo- 
gous to that by which alizarin is obtained from the monosulphonic acid. 

From alizarin there can be prepared, further, by nitration, the a- or 
/3-nitro-alizarin, and from this, by reduction, the corresponding amido- 
alizarin. From /3-nitro- and amido-aiizarin, by heating with glycerol 
and sulphuric acid, the important Alizarin Blue is obtained. Further, 
by the action of fuming sulphuric acid on alizarin there is obtained a 
tetraoxyanthraquinone (Bordeaux), etc. 



45. REACTION: ZINC DUST DISTILLATION 

Example : Anthracene from Alizarin or Quinizarin 

To a paste prepared by rubbing up ioo grammes of zinc dust 
with 30 c.c. of water, add pieces of porous pumice stone of a size 
that will conveniently pass into a combustion tube, and stir them 
around so that they become covered with the zinc dust paste. 
They are removed from the paste with pincers, heated in a porce- 
lain dish over a free flame (in constant motion) until the water is 
evaporated. A combustion tube of hard glass 60-70 cm. long 
is drawn out at one end to a narrow tube, the narrowed end is 
closed by a loose plug of asbestos, and a layer of zinc dust 5 cm. 
long is placed next to the plug ; then follows a mixture of \-\ 
gramme of alizarin or quinizarin with 10 grammes of zinc dust, 
and finally, a layer of pumice-zinc dust 30 cm. long. After a 
canal has been formed over the zinc dust, by placing the tube in 
a horizontal position and tapping it, the tube is transferred to a 
combustion furnace inclined at an oblique angle, and dry hydrogen 



33^ 'SPECIAL PART 

is passed through the tube without heating. In order to test 
whether the air has been completely expelled from the tube, the 
open end is closed by a cork bearing a small glass tube to which 
is attached a piece of rubber tubing ; the gas being evolved is 
conducted into a soap solution, and the bubbles formed are 
ignited, during which the greatest care must be taken to keep 
the flame from coming in contact with the gas issuing from the 
rubber tubing, otherwise a serious explosion may result. If an 
explosion accompanied by a report takes place when the bubbles 
are ignited, the air has not been completely removed, but if they 
burn quietly, then only pure hydrogen is present. 1 When this is 
the case, the current of gas is diminished so that only two bubbles 
per second pass through the wash-bottle ; the pumice-zinc dust 
is then heated with small flames, these are increased in size 
gradually, and finally, the tiles being placed in position, it is 
heated as strongly as possible ; then the rear layer of 5 cm. of 
zinc dust is similarly heated, and as soon as this glows, as in the 
nitrogen determination, the mixture of the substance and zinc 
dust is gradually heated. The anthracene formed condenses to 
crystals in the forward cool part of the tube. After the reaction 
is complete, while the tube is allowed to cool, a moderately rapid 
current of hydrogen is passed through it ; the forward part of the 
tube containing the anthracene is broken off and the substance 
removed with a small spatula ; it is purified by sublimation in a 
suitable apparatus (see pages 14 and 15). Melting-point, 213 . 
The sublimed anthracene is dissolved by heating in a test- 
tube with a little glacial acetic acid ; it is treated with about 
double its weight of chromic anhydride, and heated a short time 
to boiling. The solution is then diluted* with several times its 
volume of water, the anthraquinone separating out is filtered off, 
washed with some dilute sulphuric acid, then with water, and is 
finally crystallised in a test-tube from a little glacial acetic acid. 
Long colourless needles of anthraquinone, which melt at 277 , are 
thus obtained. 



1 As described under Carbon Monoxide, the test may also be made by filling a 
test-tube with the gas over water, and applying a match to the mcuth of the tube. 



PYRIDINE SERIES 337 

Zinc dust is, especially at high temperatures, an excellent reducing 
agent (Baeyer, A. 140, 295), which can be used for the reduction of 
almost all aromatic oxygen compounds derived from hydrocarbons, e.g. : 

C 6 H 6 . OH + Zn = C 6 H 6 + ZnO 

Phenol Benzene 

C 10 H 7 . OH + Zn = C 10 H 8 + ZnO 

Naphthol Naphthalene 

Also ketone-oxygen, as the above example shows, can be replaced 
by hydrogen. The reaction given under Alizarin possesses an historical 
interest, since, by means of it, Grabe and Liebermann, in 1868, dis- 
covered that alizarin, which had been previously obtained from madder 
root, was a derivative of anthracene, and could be prepared synthetically 
from it. (B. 1, 43.) 



III. PYRIDINE OR QUINOLINE SERIES 

1. REACTION: THE PYRIDINE SYNTHESIS OF HANTZSCHi 

Example : Collidine = Trimethylpyridine 

Dihydrocollidinedicarbonic Acid Ester. — A mixture of 25 
grammes of acetacetic ester and 8 grammes of aldehyde-ammonia 
is heated in a small beaker on a wire-gauze, about three minutes, to 
100-110 , the mixture being stirred with the thermometer. The 
warm reaction-mixture is then treated with double its volume 
of dilute hydrochloric acid, and stirred vigorously without further 
heating until the liquid mass solidifies. It is then thoroughly tritu- 
rated in a mortar, filtered, washed with water, and dried, either 
by pressing out, or by warming on the water-bath. For the further 
working up of the collidinedicarbonic acid ester, the crude product 
can be directly used. In order to obtain the dihydroester in a 
crystallised condition, 2 grammes of the crude product are dissolved 
in a small quantity of alcohol in a test-tube, by heat, and allowed 



1 A. 215, 1. 
z 



338 



SPECIAL PART 




Fig. 8 i. 



to cool slowly. Colourless tablets with a bluish fluorescence are 
thus obtained. Melting-point, 13 1°. 

Collidinedica7'bonic Acid Ester. — The crude dihydroester is 
treated in a small flask with an equal weight of alcohol ; complete 

solution does not take place. 
Into the mixture cooled by 
water pass nitrous fumes (Fig. 
81), until the dihydroester goes 
into solution, and a test-portion 
dissolves to a clear solution in 
dilute hydrochloric acid. The 
alcohol is then evaporated by 
heating on the water-bath, the 
thick residue is treated with a 
sodium carbonate solution to 
alkaline reaction ; the oil sepa- 
rating out is taken up with ether. 
After the ethereal solution has 
been dried by a small piece of potassium hydroxide, or potash, 
the ether is evaporated, and the residue subjected to distillation ; 
on account of the high boiling-point of the ester, a fractionating 
flask is selected, having the condensation tube as near as possible 
to the bulb. The fraction passing over between 290-3 io° can be 
used for the following experiment : 

Potassium Collidine Dicarbonate. — The saponification of the 
ester is effected by boiling with alcoholic potash, prepared in the 
following manner : Finely pulverised potassium hydroxide (2 parts 
to 1 part of ester) is moderately heated in a flask on a wire-gauze 
with 3 times its weight of absolute alcohol, until the greater portion 
has passed into solution. The alcoholic solution is then poured 
off from the portion remaining undissolved, treated with the ester 
to be saponified, and heated 4-5 hours on a rapidly boiling water- 
bath (with reflux condenser) ; the potassium salt separates out in 
crusts. The alcoholic liquid is then poured off from the salt, 
and the latter washed on the filter with alcohol and finally with 
ether. 



PYRIDINE SERIES 339 

Collidine. — The dried potassium salt is intimately mixed in a 
mortar with double its weight of slaked lime, and placed in one 
end of a hard glass tube (about 2 cm. wide and 55 cm. long). 
In order to prevent the mixture from being carried over into the 
receiver on heating, a small, loose plug of asbestos is placed in the 
tube in front of it. After a canal has been made by tapping, 
the tube is connected with an adapter bent downwards, by means 
of a cork or asbestos paper ; it is then transferred to a combustion 
furnace, the rear end of which is somewhat elevated and warmed 
throughout its entire length with small flames, beginning at the 
closed end. The flames are steadily increased in size until, with 
the tiles in position, the tube is heated as strongly as possible. 
The collidine passing over is taken up with ether, dried with 
potassium hydroxide, and, after the evaporation of the ether, is 
subjected to distillation. Boiling-point, 172 . 

On heating acetacetic ester with aldehyde-ammonia, the following 
reaction takes place (see A. 215, 8) : 



CH 3 



CH 3 
I 
/ CH \ 



OCH C 2 H 5 O.OC.C C.CO.OC 2 H 6 

C 2 H 5 O.OC.CH 2 CH 2 .CO.OC 2 H 5 = || || 

I I CH 3 — C C— CH 3 

CH3.CO CO.CH3 \xr/ 

HNH 2 N 

H + 3 H 2 0. 

Dihydrocollidinedicarbonicethyl ester 

The reaction may be modified by using other aldehydes instead of acet- 
aldehyde ; thus there is obtained from benzaldehyde, acetacetic ester, 
and ammonia, the dihydrophenyllutidinedicarbonic ester : 

C 6 H 5 CeHs 

OCH / CH \ 

C 2 H 5 . OC— CH 2 CH 2 — CO . OC 2 H 5 = C 2 H 5 . OC— C C— CO . OC 2 H 5 

II II II 

CH 3 — CO CO— CH 3 H 3 C— C C— CH 3 

X nh/ +3H20 . 



340 SPECIAL PART 

With proprionic aldehyde, butyraldehyde, valeraldehyde, oenanthol, 
myristic aldehyde, nitrobenzaldehyde, phenylacetaldehyde, furfurol, 
and others, the reaction can be carried out. All the compounds 
obtained contain the methyl groups of the two acetacetic ester mole- 
cules, but the third side-chain is different, depending upon the nature 
of the aldehyde employed. 

By passing nitrous fumes into an alcoholic solution of the dihydro- 
ester, two hydrogen atoms, and those particular hydrogen atoms in 
combination with carbon and nitrogen in the methenyl- and imido- 
groups, respectively, will be oxidised off, and there is formed a deriva- 
tive of pyridine, containing no ring hydrogen. While the dihydro- 
esters possess no basic properties, the pyridine derivative dissolves in 
acid. Therefore, by treating the solution with hydrochloric acid, it 
can be determined whether any unchanged dihydroester (insoluble in 
acid) is present. 

Concerning the saponification of the ester, refer to what was said 
under Reaction 36. 

The splitting off of carbon dioxide from a carbonic acid, or a salt 
of a carbonic acid, is generally designated as a " pyro-reaction. 1 ' For 
this kind of action a calcium salt is most frequently used ; this is mixed 
with slaked lime and subjected to distillation, e.g. : 



caO|H = C fi H ft + CaCO a . 



Calcium benzoate 

(ca=i Ca) 



In poly-basic acids, all the carboxyl groups can be replaced by hydro- 
gen. In this way an acid may be transformed into the hydrocarbon 
from which it was derived. In the above case, the potassium salt may 
be used instead of the calcium salt. 



2. REACTION: SKRAUP'S QUINOLINE SYNTHESIS 

Example : Quinoline 

In a flask of about i-i litres capacity containing a mixture of 
24 grammes of nitrobenzene, 38 grammes of aniline, and 120 
grammes of glycerol, add, with stirring, 100 grammes of concen- 
trated sulphuric acid. The flask is then connected with a long, 
wide reflux condenser, and heated on the sand-bath. As soon 



QUINOLINE SERIES 34 1 

as the reaction begins, which is recognised by the sudden evolu- 
tion of bubbles of vapour ascending through the liquid, the flame 
is removed, and the energetic reaction is allowed to complete 
itself without further heating from without. When the reaction- 
mixture has become quiet, it is again heated for three hours on 
the sand-bath, diluted with water, and from the acid liquid the 
unchanged nitrobenzene is removed with steam. As soon as no 
drops of oil pass over, the distillation with steam is discontinued. 
The liquid remaining in the distillation flask is allowed to cool 
somewhat, and then made alkaline with concentrated caustic soda 
solution, upon which the liberated quinoline, mixed with the 
unchanged aniline, is distilled over with steam. Since these sub- 
stances cannot be separated by fractional distillation, their separa- 
tion must be effected by a chemical method. For this purpose 
the distillate (oil and water solution) is treated with dilute sulphuric 
acid until all oil is dissolved and an excess of the acid is present ; 
to the cold solution a solution of sodium nitrite is added until a 
drop of the liquid will cause a blue spot on potassium iodide-starch 
paper ; if the blue colour does not appear, add more sulphuric 
acid to the mixture. The aniline (primary amine) is converted 
into diazobenzenesulphate, while the tertiary quinoline remains 
unchanged. The mixture is heated for some time on the water- 
bath, by which, as in Reaction 8, the diazo-sulphate is converted 
into phenol. The liquid is again made alkaline, upon which the 
phenol goes into solution, while the quinoline is liberated. The 
mixture is now distilled with steam, and the quinoline is obtained 
in a pure condition : it is taken up with ether, the ether evaporated, 
and the residue distilled. Boiling-point, 23 7 . Yield, 40-45 
grammes. (See Wiener Monatshefte 2, 141.) 

Quinoline is formed in the above reaction according to the following 
equation : 

H CH9.OH ti TT 

H A H \CH.0H H /V\ H 

A A I +0= I I 1 +4H.O 

W CHs - CH H\A/ H 

a imh 2 H N 

Quinoline 



342 SPECIAL PART 

The oxygen necessary for the reaction is taken from the nitrobenzene, 
which is hereby reduced in a manner that is not wholly clear. It is 
possible that the reaction may take place in this way : first, acrolein is 
formed from glycerol, under the influence of sulphuric acid : 

CH 9 .0H CH, 

I II 

CH.OH =CH +2H 2 0. 

I I 



Like all aldehydes, this condenses with aniline to form acrole'in- 
aniline. 

C (i H 5 . NH 2 + CHO . CH = CH 2 = C 6 H 5 . N=CH— CH=CH 2 + H 2 . 

While this, under the influence of the oxidising action of the nitro- 
compound, loses two atoms of hydrogen, and thus quinoline is formed : 



+ HCH\ 




CH |+H 2 0. 



The Skraup reaction is capable of a very many-sided application. 
If, instead of aniline, its homologues are used, methyl-, dimethyl-aniline, 
etc., the corresponding quinoline is obtained. Also halogen-, nitro-, 
etc., substituted amines, yield halogen-, nitro-, etc., substituted quino- 
lines. Amidocarbonic acids, amidosulphonic acids, amidophenols, yield 
carbonic acid-, sulphonic acid- or oxy-derivatives of quinoline. The 
reaction is also applicable to the corresponding amido-compounds of 
the naphthalene series. By starting from the diamines, two new pyri- 
dine rings, connected with the benzene ring, are formed ; in this way 
the so-called phenanthrolines, etc., are obtained. 

Of technical and historical interest is the discovery which was made 
by Prudhomme in the year 1877, that /2-nitroalizarin, on heating with 
glycerol and sulphuric acid, yields a blue dye, Alizarin Blue. This 
gave the impetus to Skraup's synthesis. To Grabe's investigations we 
are indebted for the knowledge of the process by which, as above, a 
quinoline synthesis is effected in the following way : 



HYDROCHLORIC ACID 



343 







OH 






OH 


CO x/ I n ^ oh /V- C °\A_oh 






...-*■ 








\/\coA/ LN02 V\oAAn 


Nitroalizarin 


1 1 


\CE\ JCH] 


\ 


CH 








Residue of the glycerol added 
Alizarin Blue 



IV. INORGANIC PART 



1. CHLORINE 



A flask is one-third filled with manganese dioxide (pyrolusite) 
in pieces the size of filberts ; to this is added a quantity of con- 
centrated hydrochloric acid which is just sufficient to cover it. 
On heating the mixture on a wire gauze with a free flame, a regular 
current of chlorine is generated ; this is passed through two wash- 
bottles containing water and concentrated sulphuric acid respect- 
ively; the water retains any hydrochloric acid which is carried 
along with the gas, and the sulphuric acid dries it. (See Figs. 74 
and 87.) A piece of thin asbestos-paper is placed on the wire 
gauze, as is always done on heating large flasks, by which the 
danger of breaking is essentially diminished. A very regular 
current of chlorine can also be obtained from finely pulverised 
potassium dichromate and crude concentrated hydrochloric acid 
by heating the mixture on the water-bath. To 1 litre of hydro- 
chloric acid, use 180-200 grammes of pulverised potassium 
dichromate. 



2. HYDROCHLORIC ACID 



Gaseous hydrochloric acid, which is frequently needed for the 
preparation of acid- esters, is generated most conveniently in a 



344 



SPECIAL PART 



Kipp apparatus charged with fused ammonium chloride in pieces 
as large as possible, and concentrated sulphuric acid. The opera- 
tion is conducted in the same way as that for the generation of 
carbon dioxide or hydrogen from a Kipp apparatus. 

If the apparatus is not available, the acid can be generated very 
conveniently in the following manner : 

In concentrated hydrochloric acid contained in a suction flask 
allow to flow from a separating funnel concentrated sulphuric acid, 
drop by drop (Fig. 82). The hydrochloric acid evolved is dried 
by passing it through concentrated sulphuric acid contained in a 





Fig. 82. 



Fig. 83. 



safety wash-bottle (Fig. 83) ; this latter is always used, since 
otherwise, with an irregular gas current, the liquid to be saturated 
may be easily drawn back into the wash-bottle and then into the 
generating mixture. In place of a WoulrT-flask with three tubu- 
lures, a single-neck wash-bottle may be converted into a safety- 
bottle as follows (see Fig. 84) : Into a two-hole cork place a 
straight tube as wide as possible ; through this insert a narrow 
delivery tube, bent at a right angle, which reaches almost to the 
bottom of the bottle. 

The liquid to be saturated cannot flow back into the wash- 
bottle with this arrangement, since in case there should be a 
tendency to do so, air would enter the suction-flask through the 
space between the delivery tube and the wider tube, thus relieving 



HYDROBROMIC ACID 



345 



the pressure. If a wash-bottle having a side-tube is available, it 
can also be converted into a safety-tube (see Fig. 85). 





Fig. 84. 



Fig. 85. 



Hydrochloric acid gas may also be obtained by warming 10 
parts of sodium chloride with a cold mixture of 3 parts of water 
and 18 parts of concentrated sulphuric acid. 

3. HYDROBROMIC ACID (see Brombenzene) 

The hydrobromic acid obtained as a by-product in the bromina- 
tion reactions is purified by distilling it from a fractionating flask. 
Water first passes over until finally the temperature remains con- 
stant at 1 2 6°, when a 48 % acid goes over ; this is collected. 

In order to prepare potassium bromide for use in the prepara- 
tion of ethyl bromide, the acid is diluted with some water and 
then treated with dry potash until there is no further evolution of 
carbon dioxide and the liquid shows a neutral reaction. To 
1 part of hydrobromic acid 0.5 part potassium carbonate is used. 
The water solution of the potassium bromide is evaporated to dry- 
ness on a water-bath. The product thus obtained may be used 
directly for the preparation of ethyl bromide. 

4. HYDRICDIC ACID 

To 44 grammes of iodine (not pulverised) contained in a small 
round flask of about 100 c.c. capacity (Fig. 86), gradually add 
4 grammes of yellow phosphorus divided into about 8 pieces ; 



346 



SPECIAL PART 



these are dried just before transferring them to the flask, by press- 
ing between layers of blotting-paper. The first piece of phos- 
phorus added unites with the iodine with an active evolution of 
heat and light. When the first action is ended, after shaking the 
contents of the flask, which soon become liquid, the second piece 
is added. The reaction still proceeds with evident energy, al- 
though it is less intense than when the first piece was added. 
Care is taken to place the phosphorus as nearly as possible in the 
middle of the flask, and not to allow it to fall on the walls, since 
otherwise the flask may be easily broken. When all of the phos- 
phorus is added, a fused, dark mass of phosphorus triiiodide is 
obtained which becomes solid on cooling. The hydriodic acid pre- 
pared from this by warming with 
water, must be passed over red 
phosphorus in order to free it 
from iodine which is carried 
along with it. Proceed as fol- 
lows : 5 grammes of red phos- 
phorus are rubbed up to a paste 
with 2 c.c. of a water solution 
of hydriodic acid, or in case this 
is not available, with as little 
water as possible (i c.c. at the 
most). In this is placed glass 
beads, or bits of broken glass, 
which on stirring around in the mixture become covered with the 
paste. They are then transferred to a U-tube. In order to prepare 
a water solution of hydriodic acid, the gas issuing from the U-tube 
is passed into 45 c.c. of water (see Fig. 86). The glass tube is not 
immersed in the water, but its end must be 1 cm. above the surface ; 
otherwise, in consequence of the great affinity of water for hydriodic 
acid, under certain conditions the water may be drawn back. 

The hydriodic acid is now obtained by treating the completely 
cooled phosphorus triiodide with 6 grammes of water and warm- 
ing with a very small luminous flame. The contents of the flask 
steadily become clearer, while in the other flask the heavy layer 




Fig. 86. 



HYDRIODIC ACID 347 

of hydriodic acid sinks to the bottom. The heating is continued 
until only a clear, colourless liquid remains in the generating flask. 

In order to obtain a concentrated solution of hydriodic acid, 
the liquid in the receiver is distilled. At first a few cubic centi- 
metres of water pass over at ioo°, then the temperature rises in 
a short time to 125 ; the concentrated acid passing over up to 
130 is collected separately. This boils for the most part at 127 . 

This experiment teaches much concerning the chemistry of 
phosphorus and iodine. First, it shows that iodine and phos- 
phorus unite directly with a vigorous reaction, to form phosphorus 
triiodide : 

The iodide then decomposes with water, to form hydriodic acid, 
which is evolved, while the phosphorous acid (H 3 P0 3 ) remains in 
the flask : 



P I 3 + 3H .OH = 3HI + PH 3 3 



The gaseous hydriodic acid is an intensely fuming substance, 
which may be easily shown by removing the cork from the 
receiver containing the aqueous acid, for a moment. Hydriodic 
acid is absorbed by water with great avidity. The acid, boiling 
constantly at 127 , contains approximately 50% of anhydrous 
hydriodic acid. 

In this experiment it is observed that the connecting tubes of 
the apparatus, especially those between the generating flask and 
the U-tube become coated with crystals of a diamond-like bril- 
liancy. These are crystals of phosphonium iodide, PH 4 I, which is 
formed by the decomposition of phosphorous acid. 

It is a common property of all the lower oxidation products 
of phosphorus, to pass over to the highest oxidation product — 
phosphoric acid, with the evolution of phosphine on heating. 
With phosphorous acid, the reaction takes place as follows : 
4 PH 3 3 = 3 H 3 P0 4 + PH 3 . 

The phosphine thus formed unites, since it possesses weak basic 
properties, with hydriodic acid, to form phosphonium iodide : 
PH 3 + HI = PH 4 I . 



348 SPECIAL PART 

Since this may easily clog the connecting tubes, the tubes 

selected are as wide as possible. On cleaning the tubes with 

water, this reacts with the phosphonium iodide with the evolution 

of phosphine, a gas with a garlic-like odour, and which in this 

case is not spontaneously inflammable. The phosphonium iodide 

decomposes with water into its components, in accordance with 

this equation : 

PH 4 1 + H 2 = PH 3 + HI . 

This reaction, as is well known, is employed for preparing pure 
phosphine which is not spontaneously inflammable. 

5. AMMONIA 

Gaseous ammonia is prepared most conveniently by heating 
the most concentrated ammonia solution in a flask over a wire 
gauze with a small flame. In order to dry the gas, it is passed 
through a drying tower filled with soda-lime. (See Fig. 66.) 

6. NITROUS ACID 

For the preparation of gaseous nitrous acid, arsenious acid, 
broken into pieces the size of a pea, is treated with nitric acid, 
sp. gr. 1.3, and heated gently on a wire gauze with a free flame 
(under the hood) . In order to condense the nitric acid carried 
along with the gases, an empty wash-bottle, cooled by cold water, 
is employed. (See Fig. 81.) 

7. PHOSPHORUS TRICHLORIDE 

Under water, in a porcelain mortar, cut 40 grammes of yellow 
phosphorus, with a knife or chisel, into pieces which will con- 
veniently pass into the tubulure of a 300 c.c. retort. After the air 
in the retort has been displaced by dry carbon dioxide (Fig. 87), 
each single piece of phosphorus is taken from the water by pincers, 
and dried quickly by pressing it between several layers of filter- 
paper, and immediately placed in the retort, care being taken to 
prevent it from becoming ignited by friction in the opening of 
the tubulure. As soon as all the phosphorus has been transferred 



PHOSPHORUS TRICHLORIDE 



349 



to the retort, the tubultire is connected with a delivery tube which 
must move easily in the cork, and a moderately rapid current of 




dry chlorine passed over the phosphorus ; phosphorus chloride is 
thus formed with evolution of heat and light. If crystals of phos- 
phorus pentachloride should collect in the neck of the retort, the 



35o 



SPECIAL PART 



delivery tube is pushed somewhat farther into the retort. If, on 
the other hand, phosphorus distils to the upper part of the retort, 
the tube is somewhat raised. The phosphorus trichloride con- 
densing in the receiver is distilled from a dry fractionating flask. 
Boiling-point, 74 . Yield, 125-140 grammes. 



8. PHOSPHORUS OXYCHLORIDEi 

To 100 grammes of phosphorus trichloride, contained in a large 
tubulated retort connected with a condenser, add gradually, in 
small portions of about 2-3 grammes, 
32 grammes of finely pulverised potas- 
sium chlorate. After each addition, 
wait until the liquid bubbles up, before 
adding a new quantity. - If, on the 
addition of the first portion, no reac- 
tion takes place, it is started by a gentle 
warming. During the addition, no 
liquid should distil into the receiver, 
but if this does happen, it is poured 
back into the retort. After all of the 
chlorate has been added, the phos- 
phorus oxychloride formed is distilled, 
by heating the retort in an oil-bath, 
to 130 , or with a luminous flame. A 
suction-flask is used as a receiver; 
this is firmly connected with the end 
of the condenser, by means of a cork. 
The distillate is rectified from a frac- 
tionating flask provided with a thermometer. Boiling-point, no c 
Yield, 100-1 10 grammes. 




fig. 



9. PHOSPHORUS PENTACHLORIDE 

Through the upper delivery tube of an apparatus similar to that 
represented in Fig. 88, a stream of dry chlorine is admitted, which 

1 J. pr. Ch. 1883, [2] Vol. 28, 382. 
Y 



SULPHUROUS ACID 35 I 

passes out of the lower, right-angled tube. From time to time, 
several cubic centimetres of phosphorus trichloride are allowed to 
flow into the bottle from a separating funnel, upon which the 
trichloride unites with the chlorine to form the solid pentachloride. 
Since this operation can be repeated, as soon as it is evident that 
the union is completed, any desired quantity of phosphorus penta- 
chloride can be prepared. Should the delivery tube become 
stopped up, it is cleared by the glass rod with which the apparatus 
is provided. As the quantity of the pentachloride formed in- 
creases, the tube is correspondingly raised. Yield, quantitative. 

10. SULPHUROUS ACID 

Gaseous sulphurous acid is generated in an apparatus similar to 
the one represented in Fig. 82, by adding to a concentrated water 
solution of sodium hydrogen sulphite a cold mixture of equal parts, 
by volume, of water and concentrated sulphuric acid, drop by drop. 
The generating flask is shaken frequently, to keep the contents 
from separating into layers. 

11. SODIUM 

(a) To cut Sodium. — In order to divide sodium into small 

portions, it can be cut into scales with a knife, or pressed out into 

a wire with a sodium-press. To cut it into scales, an apparatus 

similar to that represented in Fig. 89 is convenient. After both 

-^ sides of the knife and the front part 

'^^^Esmi °^ t ^ ie ta ^ e have been coated with 

1 r^"^ a ^ m l aver of vaseline, a long stick 

^^^^--~- of the metal to be cut, the end of 

YJ-fi^SOkJi which ^ wrapped in filter-paper, in 

/i| lLJ*nG!t^^N. order that it may be handled, is 

L. J>^b> placed on the table so that it projects 

^^fc-^g ^ » ^ somewhat over the front end; it is 

FlG - 89# then cut with a short stroke of the 

knife. On the front part of the lower platform is placed a small 

dish filled with ether or ligroin, into which the scales fall. When 



35 2 SPECIAL PART 

using the knife, two points are to be especially observed. The 
eye is never placed in front of the knife, but always behind it, so 
that the fingers holding the sodium can always be seen. Only in 
this way can a wound be prevented. Further, the cross-section 
of the piece of sodium must not be too large, otherwise the metal 
adheres to the knife. Quadratic scales, the edge of which must 
not, at most, be more than 5-6 mm. long, are cut. With a little 
practice, large quantities of the metal can be cut in very thin 
scales in a short time. 

The sodium residues are not thrown into water nor into waste- 
jars, but are dropped into alcohol contained in a beaker or flask. 

(b) Sodium Amalgam. — Sodium scales, about the size of a 
20-cent piece, are pressed to the bottom of mercury contained in 
a porcelain mortar, in rather rapid succession, by means of a short, 
moderately thick glass rod, drawn out to a point and bent at a 
short right angle. The scales are speared on the glass rod (under 
the hood ; eyes protected by spectacles ; hands, with gloves) . 

The mercury may also be warmed in a porcelain casserole on 
the water-bath (60-70 ), and, without further heating, small 
pieces of sodium, the size of a half bean, are thrust to the bottom 
of the vessel with the aid of a glass rod. 

12. ALUMINIUM CHLORIDE 

A wide tube, diameter 1^-2 cm., of hard glass drawn out to 
a narrow tube, is at one end connected by means of a cork 
with a wide-neck so-called "salt bottle" (Fig. 90). The cork 
with which this is closed is supplied with a second, smaller hole, 
bearing a delivery tube of at least 8 mm. diameter, extending 
to the centre of the receiver. The tube is half filled (half of 
its cross-section) with aluminium shavings, which have been 
previously freed from oil by boiling with alcohol and then dried 
in an air-bath at 120 ; an asbestos plug is placed at each end 
of the layer. A rapid current of hydrochloric acid gas, most 
conveniently obtained from a Kipp apparatus charged with fused 
ammonium chloride and concentrated sulphuric acid, is passed 



ALUMINIUM CHLORIDE 



353 



through the apparatus. Care must be taken that the drying flask 
containing sulphuric acid is not too small, since the acid foams 
easily. As soon as the air is driven out of the apparatus, — this 
has been accomplished when the gas evolved is completely 
absorbed by water (a piece of rubber tubing is attached to the 
tube, and the gas tested from time to time by immersing the end 
of the tubing in water in a beaker), — the tube is heated in a com- 
bustion furnace throughout its entire length, at first with small 
flames, which are gradually increased (Fig. 90). When the flames 
have reached a certain size, white vapours of aluminium chloride, 
condensing in the receiver, are noticed. The reaction is ended 
as soon as the aluminium, except for a small, dark-coloured resi- 



-J 



3ffnr 



(F=* 




B* 



Fig. 90. 



due, disappears. For the success of the preparation, the following 
points are particularly observed: (1) All parts of the apparatus 
must be perfectly dry. (2) The air must be removed as com- 
pletely as possible, since, otherwise, an explosion of oxygen and 
hydrogen may take place. (3) The portion of the tube extend- 
ing beyond the furnace must be as short as possible, to prevent 
the aluminium chloride from condensing in it, which results in a 
stopping up of the apparatus. In order that the cork may not 
burn, it is protected by an asbestos plate, provided with a circular 
hole in the centre. (4) The aluminium must not be heated to 
melting. If this should happen at any particular point, the flames 
must be immediately lowered. (5) The hydrochloric acid cur- 
rent must be extremely rapid. One should not be able to count 
single bubbles of the gas, but they should follow one another 



354 SPECIAL PART 

uninterruptedly. The evolution of a small quantity of a smoky 
vapour from the outlet-tube will always occur, but the greatest 
part of the aluminium chloride is condensed even if the hydro- 
chloric acid rushes through the wash-bottles. Should the first 
experiment be unsuccessful, in consequence of a stoppage of the 
tube, the method for correcting this will readily suggest itself. 

Recently it has been shown that it is better to use for the re- 
ceiver an iron tube 25 cm. long and 4 cm. wide (inner diameter). 
To one end of this is welded a narrower tube, 2 cm. long; by 
filing it on the inside the end is given a somewhat conical shape ; 
it is selected of such a diameter that the glass tube can be fastened 
in it with a few turns of asbestos paper. The end not narrowed 
is closed by a cork bearing a glass tube as wide as possible lead- 
ing to the hood. A receiver of this kind is advantageous because 
the glass tube can be heated strongly to its extreme end, and thus 
a stopping up of the apparatus may be entirely prevented. If the 
iron tube should become too hot, a wet towel is placed on it and 
moistened from time to time. 

The aluminium chloride condensing in the receiver is preserved 
in well-closed bottles, or best, in a desiccator. 

13. LEAD PEROXIDE 

In a large porcelain dish dissolve, with heat, 50 grammes of 
lead acetate in 250 c.c. of water, and treat with a solution of 
bleaching-powder, prepared by shaking 100 grammes of bleaching- 
powder with \\ litres of water and filtering, heat not quite to 
boiling, until the precipitate, bright at first, becomes deep dark 
brown. A small test-portion is then filtered hot, and the filtrate 
treated with the bleaching-powder solution and heated to boiling ; 
if a dark brown precipitate is formed, more of the bleaching- 
powder solution is added to the main quantity, and it is heated 
until a test gives no precipitate with the bleaching-powder solution. 
The main quantity of the liquid is separated from the heavy pre- 
cipitate by decantation ; the latter is washed several times with 
water (decantation), and then filtered with suction; the precipi- 



LEAD PEROXIDE 355 

tate is washed repeatedly with water. The lead peroxide is not 
dried, but is preserved in a closed vessel in the form of a thick 
paste. 

Value Determination. — In order to determine the value of the 
paste, a weighed portion is heated with hydrochloric acid, the 
chlorine evolved is passed into a solution of potassium iodide, 

N 
and the liberated iodine is titrated with a — solution of sodium 

10 

thiosulphate (refer to a text-book on Volumetric Analysis). The 
determination, carried out as follows, is sufficiently accurate for 
preparation work : On an analytical balance weigh off exactly 6.2 
grammes of pure, crystallised sodium thiosulphate ; this is dis- 
solved in enough cold water to make the volume of the solution 
just 250 c.c. In a small flask weigh off 0.5-1 gramme of the 
peroxide paste \ treat this (with cooling) with a mixture of equal 
volumes of concentrated hydrochloric acid and water ; the flask 
is immediately connected with a delivery tube, and this is inserted 
in an inverted retort, the neck of which has been expanded to a 
bulb, and which contains a solution of four grammes of potassium 
iodide in water. When heat is applied to the flask, chlorine is 
generated, which liberates iodine from the potassium iodide. 
After the end of the heating, care is taken that the potassium 
iodide solution is not drawn back into the flask. The contents 
of the retort are then poured into a beaker and treated with the 
thiosulphate solution from a burette until the yellow colour of 
the iodine just disappears. Since a molecule of the peroxide 
liberates two atoms of iodine, a cubic centimetre of the thiosul- 
phate solution corresponds to — — — = .012 gramme pure lead 
peroxide. 

14. CUPROUS CHLORIDE 

Heat a solution of 50 grammes of copper sulphate and 24 
grammes of salt to 60-70 . Into this conduct a current of sulphur 
dioxide until the precipitate of cuprous chloride no longer increases. 
The precipitate is filtered with suction and washed, first with sul- 



356 



SPECIAL PART 



phurous acid and then with glacial acetic acid until it runs through 
colourless. The moist preparation is then heated in a shallow 
porcelain dish or a large watch crystal on the water- bath until the 
odour of acetic acid cannot be detected. It is preserved in a well- 
closed flask. 

15. DETERMINATION OF THE VALUE OF ZINC DUST 

From a weighing- tube pour into a ioo c.c. round flask o.i 
gramme zinc dust (exact weighing) and add a few cubic centi- 
metres of water. The flask is closed by a good three-hole cork. 
In the middle one is inserted a small dropping funnel ; the side 
holes carry the inlet and outlet tubes (Fig. 91). The stem of 
the funnel is previously filled with water by open- 
ing the cock, immersing the end in water and 
applying suction. The inlet tube is connected with 
a Kipp carbon dioxide generator, and the outlet 
tube with a nitrometer charged with a solution of 
caustic potash. Carbon dioxide is passed into the 
apparatus until all the gas escaping from the outlet 
tube is absorbed by the potash. The current of 
carbon dioxide is then lessened and from the drop- 
ping funnel a mixture of 10 c.c. of concentrated 
hydrochloric acid and 10 c.c. water containing a 
few drops of platinic chloride, is allowed to flow in on the zinc 
dust ; the flask is finally heated. From the volume of hydrogen 
obtained the percentage of zinc in the zinc dust may be calcu- 
lated. The individual operations of this analysis are conducted 
as described under " Determination of Nitrogen." 




Fig. 91. 



INDEX 



Abbreviations, 360. 
Acetacetic ester, 156. 
Acetaldehyde, 143. 
Acetamide, 1 31. 
Acetic anhydride, 127. 
Acetic ester, 137. 
Acetonitrile, 135. 
Acetyl chloride, 121. 
Active mandelic acid, 281. 
Aldehyde, 143. 
Aldehyde-ammonia, 145. 
Alizarin, 333. 
Aluminium chloride, 352. 
Amidoazobenzene, 238. 
Amidodimethyl aniline, 231. 
Ammonia, 348. 
Ammonium eosin, 326. 
Aniline, 188. 
Animal charcoal, 45. 
Anthracene, 335. 
Anthraquinone, 336. 
Antipyrine, 228. 
Autoclaves, 63. 
Azines, 274. 
Azobenzene, 199. 
Azo dyes, 229. 
Azoxybenzene, 199. 

Beckmann's Reaction, 292. 
Benzal chloride, 269. 
Benzaldehyde, 269. 
Benzamide, 289. 
Benzene from aniline, 210. 
Benzene from phenylhydrazine, 223. 
Benzenesulphinic acid, 258. 
Benzenesulphon amide, 253. 



Benzenesulphon chloride, 253. 
Benzenesulphonic acid, 253. 
Benzidine, 204. 
Benzil, 278. 
Benzoic acid, 274. 
Benzofcphenylester, 290. 
Benzoin, 276. 
Benzophenone, 292. 
Benzophenone oxime, 292. 
Benzotrichloride, 271. 
Benzoyl chloride, 289. 
Benzyl alcohol, 274. 
Benzyl chloride, 271. 
Bitter almond green, 322. 
Boiling-point, corrections of, 32. 
Bomb-furnace, 61. 
Bomb-tubes, 58. 
Brombenzene, 244. 
Bromethane, 112. 
Bromine carrier, 246. 
Bromine, determination of, 75. 
Bruhl's apparatus, 15, 27. 
Biichner funnel, 53. 
" Bumping," 31. 
Butlerow's Synthesis, 126. 
Butyric acid, 161. 

Carbon, determination of, 98. 
Carbon monoxide, 304. 
Chloracetic acid, 139. 
Chlorine, 343. 

Chlorine, determination of, 75. 
Cinnamic acid, 285. 
Cleaning the hands, 71. 
Cleaning vessels, 70. 
Collidine, 337. 
357 



358 



INDEX 



Collidinedicarbonic ester, 338. 
Congo-paper, 231. 
Crystallisation, I. 
Crystal violet, 330. 
Cuprous chloride, 355. 

Decolourising, 45. 
Diazoamidobenzene, 235. 
Diazobenzeneimide, 212. 
Diazobenzeneperbromide, 21 1. 
Diazo-compounds, 210. 
Diazonium compounds, 211. 
Diazotisation, 210. 
Dibrombenzene, 244. 
Dihydrocollidinedicarbonic ester, 337. 
Dimethylcyclohexenone, 177. 
Dinitrobenzene, 185. 
Diphenyliodonium iodide, 217. 
Diphenylmethane, 301. 
Diphenylthiourea, 207. 
Disazo dyes, 234. 
Distillation, 16. 
Distillation with steam, 37, 
Drying, 47. 
Drying agents, 48. 
Drying, of vessels, 70. 

Eosin, 323. 

Ether, pure, 250. 

Ethyl acetate, 137. 

Ethyl benzene, 249. 

Ethyl bromide, 112. 

Ethylidene bisacetacetic ester, 176. 

Ethylene, 166. 

Ethylene alcohol, 171. 

Ethylene bromide, 166. 

Ethyl iodide, 113. 

Ethyl malonic acid, 162. 

Ethyl malonic ester, 161. 

Extraction with ether, 43. 

Filter press, 54. 
Filtration, 51. 
Fittig's Synthesis, 249. 
fluorescein, 323. 
Fractional crystallisation, n. 
Fractional distillation, 23. 
Friedel-Crafts' Reaction, 292. 



Fuchsine-paper, 231. 

Gattermann-Koch Reaction, 303. 
Glycol, 171. 
Glycoldiacetate, 171. 
Guanidine, 207. 

Halogens, determinations of, 75. 
Heating under pressure, 58. 
Helianthine, 229. 
Hydrazobenzene, 199. 
Hydrazones, 227. 
Hydriodic acid, 345. 
Hydrobromic acid, 345. 
Hydrochloric acid, 343. 
llydrocinnamic acid, 288. 
Hydrogen, determination of, 98. 
Hydroquinone, 243. 
Hofmann Reaction, 152. 

Inactive mandelic acid, 279. 
Iodine chloride, 141. 
Iodine, determination of, 75. 
Iodobenzene, 217. 
Iodoethane, 113. 
Iodosobenzene, 217. 
Isodiazo compounds, 212. 
Isonitrile reaction, 195. 

KnoevenageFs ring closing, 176. 
Kolbe's Reaction, 316. 

Lead peroxide, 354. 

Malachite green, 320. 
Malonic ester, 161. 
Mandelic acid, 279. 
Mandelic nitrile, 279. 
Melting-point, determination of, 66. 
Methyl amine, 151. 
Methylene blue, 235. 
Michler's ketone, 330. 
Monobrombenzene, 244. 
Monochloracetic acid, 139. 

Naphthalenesulphonic acid (/3), 26r. 
Naphthol (/3), 264. 
Nitroaniline, 188. 



INDEX 



359 



Nitrobenzene, 185. 
Nitrogen, determination of, 85. 
Nitrophenol (o and p), 267. 
Nitroso benzene, 196. 
Nitrous acid, 348. 

Opening bomb tubes, 61. 
Osazones, 227. 
Oxybenzaldehyde (p), 313. 

Perkin's Reaction, 285. 
Phenol from aniline, 216. 
Phenyldisulphide, 261. 
Phenylhydrazine, 223. 
Phenylhydroxylamine, 196. 
Phenyliodide, 217. 
Phenyliodide chloride, 217. 
Phenyliodite, 217. 
Phenyl mercaptan, 260. 
Phenyl mustard oil, 206. 
Phosphorus oxychloride, 350.. 
Phosphorus pentachloride, 350. 
Phosphorus trichloride, 348. 
Pipette, capillary, 42. 
Potassium acetate, 171. 
Potassium-iodide-starch-paper, 214. 
Pressure flasks, 63. 
Pukall cells, 54. 
Pyro-reaction, 340. 

Qualitative tests for carbon, hydrogen, 
nitrogen, sulphur, chlorine, bro- 
mine, iodine, 72. 

Quantitative determination of carbon 
and hydrogen, 98. 

Quantitative determination of halo- 
gens, 75. 

Quantitative determination of nitro- 
gen, 85. 

Quantitative determination of sulphur, 
81. 

Quinizarin, 331. 

Quinoline, 340. 

Quinone, 239. 

Reduction of an azo dye, 229. 
Runge's Reaction, 194. 



Safety wash-bottle, 344. 

Salicylic acid, 316. 

Salicylic aldehyde, 312. 

' Salting out,' 44. 

Sandmeyer's Reaction, 222. 

Saponification of ethyl malonic ester, 

162. 
Schotten-Baumann Reaction, 290. 
Sealing of bomb-tubes, 58. 
Separation of liquids, 41. 
Sodium, 351. 

Sodium acetate, anhydrous, 127. 
Sodium amalgam, 352. 
Sodium eosin, 326. 
Sodium knife, 351. 
Solvents, 2. 
Steam distillation, 37. 
Sublimation, 14. 
Sulphanilic acid, 208. 
Sulphobenzide, 253. 
Sulphur, determination of, 81. 
Sulphurous acid, 351. 
Superheated steam, 40. 

Tarry matter, removal of, 45. 
Terephthalic acid, 309. 
Testing thermometers, 69. 
Tests for carbon, 72. 
Tests for halogen, 74. 
Tests for hydrogen, 72. 
Tests for nitrogen, 72. 
Tests for sulphur, 73. 
Thermometer, tests of, 69. 
Thiocarbanilide, 205. 
Thiophenol, 258. 
Toluic acid, 307. 
Tolyl aldehyde, 303. 
Tolyl nitrile, 221. 
Trimethylpyridine, 337. 
Triphenylguanidine, 206. 

Vacuum distillation, 25. 
Volhard Tubes, 63. 

Xylenol (s), 178. 

Zinc dust determination, 356. 
Zinc dust distillation, 335. 



ABBREVIATIONS 



A. = Liebig's Annalen der Chemie. 

A. ch. = Annales de chimie et de physique. 

B. = Berliner Berichte. 

Bl. = Bulletin de la societe chimique de Paris. 

Ch-Z. = Chemiker Zeitung. 

J. = Jahresbericht iiber die Fortschritte der Chemie. 

J. pr. = Journal fur praktische Chemie. 

P. = Poggendorff's Annalen. 

R. = Journal der russischen chemischen Gesellschaft. 

Z. = Zeitschrift fiir Chemie. 



360 



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